Additives for Coating Compositions and Related Methods

ABSTRACT

Disclosed are curable coating compositions, and methods of cathodic corrosion protection using the compositions. For example, a curable coating composition comprising a mixed salt of magnesium thiodialkanoate, and a method for applying the coating composition, which when applied onto a steel or other ferrous substrate provides an anticorrosive coating, effective for improving resistance to cathodic disbondment.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application Ser. No. 62/523,577, filed Jun. 22, 2017; and U.S.Provisional Patent Application Ser. No. 62/609,065, filed Dec. 21, 2017.

BACKGROUND

Metal surfaces deteriorate when exposed to certain environmentalconditions through a process referred to as corrosion. Corrosion is anatural process that converts refined metal to a more chemically-stableform, such as an oxide, a hydroxide, or a sulfide, by a chemical orelectrochemical reaction. Coatings are often used to protect metalsurfaces, but over time cathodic disbondment or delamination can occur.Cathodic disbondment or delamination is the main failure mechanism ofsteel and galvanized steel surfaces coated by organic coating layers.¹Upon permeation of water beneath the organic coating due to the passivediffusion through coating imperfections, cracks, or metallic cut edges acorrosion cell is formed that is characterized by anodic and cathodicreactions.

There exists a need to develop alternative coatings to reduce or toprevent cathodic or anodic disbondment of a coating from a metalsurface.

SUMMARY

In one aspect, disclosed herein is a curable coating compositioncomprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins.

In another aspect, provided herein are methods of anticorrosivetreatment comprising:

-   -   providing a substrate, wherein said substrate is a ferrous        substrate;    -   coating the substrate with a composition comprising:    -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins;        thereby preventing or reducing corrosion of the substrate.

In another aspect, provided herein are methods of preventing or reducingcorrosion on a surface, comprising applying to the surface a coating,comprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins;        thereby preventing or reducing corrosion of the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a scheme of a metathesis reaction between a rare earth (RE)salt and carboxylic acid.

FIG. 2 shows exemplary magnesium salts utilized as coating components inthe disclosed compositions of matter.

FIG. 3 shows a replacement reaction of metallic magnesium and3,3′-thiodipropionic acid (TDPA) or 3,3′-dithiodipropionic acid (DTDPA)in aqueous solution.

FIG. 4 shows a proton NMR (400 MHz, D₂O) spectrum of an exemplarymagnesium salt, MgAcTDPA. Proton assignments to acetate and TDPA areshown on the spectrum.

FIG. 5 shows a model composition of an exemplary mixed salt (MgAcTDPA)fraction that matches composition experimentally found from elementalanalysis.

FIG. 6 shows thermogravimetric analysis (TGA) and differential scanningcalorimetry (DSC) analysis of an exemplary salt (magnesiumthiodipropionate, MgTDPA_(1:1)), an exemplary mixed salt (MgAcTDPA), andits parent salt, magnesium acetate tetrahydrate (MgAc₂), at a 10° C./mintemperature ramp in nitrogen atmosphere. Solid and dashed lines show theweight % and heat flow, respectively.

FIG. 7 shows X-ray powder diffraction (XRPD) pattern of parent magnesium(Mg), thiodipropionic acid (TDPA), and magnesium thiodipropionateprepared with magnesium:thiodipropionate stoichiometric ratio of 1:1(MgTDPA_(1:1)) and 5:1 (MgTDPA_(5:1)).

FIG. 8 shows X-ray photoelectron spectroscopy (XPS) spectra fo the Mg 2ppeak of magnesium hydroxide (Mg(OH)₂) and MgTDPA_(1:1) (MgTDPA).

FIG. 9 shows a proton NMR (400 MHz, D₂O) spectrum of an exemplary mixedsalt (MgAcTDPA) extracted from a composite montmorillonite intercalatedwith MgAcTDPA using ethanolic solution. Proton assignments to water,acetate (H₂C<) and TDPA (H₃C−) are shown on the spectrum.

FIG. 10 shows TGA of as-received montmorillonite K 10 (M) and the sameclay loaded with an exemplary mixed salt, magnesium acetatethiodipropionate, (M/MgAcTDPA) as described in Example 2. Temperatureramps at 20° C./Min in nitrogen atmosphere. Solid and dashed lines showthe weight % and heat flow, respectively.

FIG. 11 shows SEM microphotograph of the particulates comprising thetest powder coating composition with MgTDPA as the corrosion inhibitor.

FIG. 12 shows exemplary potentiodynamic polarization curve for aspecimen of galvanized steel as the working electrode in 3.5% NaCl withMgAcTDPA (effective concentration, 2.5 mg/mL) added. pH=5.3, T=25° C.

FIG. 13 shows an exemplary Tafel plot resulting from a potentiodynamicpolarization experiment with a specimen of galvanized steel in 3.5% NaClwith MgAcTDPA (effective concentration, 8.4 mM) added. pH=5.25, T=25° C.The Tafel extrapolation depicts the corrosion potential (E_(corr)), thecorrosion current (i_(corr)), and cathodic and anodic betas.

FIG. 14 shows FTIR-ATR spectra of the galvanized steel electrode surfaceafter potentiodynamic electrochemical experiments with 3.5% NaClelectrolyte without additives and with the same electrolyte containing10 mg/mL MgTDPA_(1:1) (MgTDPA) as an additive. Vertical dotted linesindicate the following spectral assignments: 1720 cm⁻¹, C═O stretchingvibrations of TDPA⁻; 1537 cm⁻¹ and 1398 cm⁻¹, stretching vibrations ofthe carbonate ion in hydrozincite [Zn₅(CO₃)₂(OH)_(6]) and simonkolleite[Zn₅(OH)₈Cl₂.H₂O]; 1440 cm⁻¹, symmetric COO⁻ stretching of thecarboxylate anion; and 671 cm⁻¹, v_(s) (C—S) stretching vibrations ofTDPA⁻.

FIG. 15 shows FTIR spectra of as-made MgTDPA_(1:1) (MgTDPA); MgAcTDPA,and as-received TDPA.

FIG. 16 shows typical Tafel plots illustrating effect of additives onpotentiodynamic polarization of galvanized steel in 3.5% NaCl (initialpH 5.6, 25° C.). Designations, control: no additives; MgAcTDPA,MgAcTDPA_(1:1), and MgAcTDPA_(5:1) magnesium acetate thiodipropionate;and TDPA: thiodipropionic acid. Additive concentrations: 10 mg/mL.

FIG. 17A shows a typical Nyquist plot for galvanized steel in aqueous3.5% NaCl (pH 5.6, 25° C.) without additive. Circles are experimentaldatapoints, and the solid line represents simulated (modeled) spectra.Electrical equivalent circuits (EEC) used to fit the electricalimpedance spectra is shown on the spectrum. Designations on EEC are asfollows: R_(el) is the ohmic resistance between the working and thereference electrode; R_(CT) is the charge transfer resistance related tothe corrosion reaction at open-circuit potential (OCP); CPE is thecapacitance of the electric double layer at the electrode/electrolyteinterface.

FIG. 17B shows a typical Nyquist plot for galvanized steel in aqueous3.5% NaCl (pH 5.6, 25° C.) with additive, MgTDPA_(1:1). EffectiveMgTDPA_(1:1) concentration was 10 mg/mL. Squares are experimentaldatapoints, and the solid line represents simulated (modeled) spectra.EEC used to fit the electrical impedance spectra is shown on thespectrum. Designations on EEC are as follows: R_(el) is the ohmicresistance between the working and the reference electrode; R_(CT) isthe charge transfer resistance related to the corrosion reaction at OCP;CPE is the capacitance of the electric double layer at theelectrode/electrolyte interface; CPE_(p) is the pseudocapacitance andR_(p) is the pseudo-resistance of the surface-adsorbed additive (MgTDPA)layer.

FIG. 18 shows concentration dependencies of inhibition efficiency (IE,%) of MgTDPA_(1:1), MgAcTDPA, and TDPA in protecting galvanized steelfrom corrosion in 3.5% NaCl at pH 5.6, 25° C. The data were derived fromthe potentiodynamic polarization measurements performed at varyingconcentrations of additives. C_(TDPA) (mM) is the effectiveconcentration of thiodipropionate in electrolyte.

FIG. 19 shows the linearized form of Langmuir adsorption isotherms foradsorption of MgTDPA_(1:1), MgAcTDPA, and TDPA on galvanized steel at25° C. and pH 5.6. The data was obtained from FIG. 18, utilizing themean values of q=0.01·IE (n=3). In all cases, linear fits were excellent(R²>0.99).

FIG. 20 shows oscillatory shear time sweep results of the gel time testsfor ARALDITE® LY8601/ARADUR® 8602 (4:1 w/w) control epoxy curinginfusion system (ECIS) and the same system modified by composite pigmentparticulates of montmorillonite with magnesium acetate thiodipropionate(M/MgAcTDPA). Open and filled datapoints show storage (G′) and loss (G″)moduli, whereas lines show corresponding loss angle (δ°, solid line forthe ECIS resin and dotted line for the pigment-modified resin). Arrowsindicate the gel time. Temperature was 82° C. throughout.

FIG. 21 shows plots of gel time (t_(gel)) as a function of reciprocaltemperature for the ARADALITE® LY8601 epoxy/ARADUR® 8602 amine withoutadditives and with 5 wt % of MgTDPA_(1:1) or MgAcTDPA added. Arrheniusmodel coordinates were used according to expression ln(t_(gel))=lnA+(ΔE_(a)/RT), where t_(gel) (s) is the gel time, A is thepre-exponential factor, E_(a) (kJ/mol) is the activation energy, and T(K) and R (J/K.mol) are temperature and gas constant, respectively.

FIG. 22 shows a schematic of polymerization curing of an exemplarybenzoxazine resin, XU35610 resin.

FIG. 23 shows differential scanning calorimetry (DSC) data (15° C./min,under nitrogen) for bisphenol-A based benzoxazine resin XU 35610 in theabsence of accelerator/catalyst and in the presence of MgAcTDPA (12 wt%).

FIG. 24 shows DSC curing exotherms of benzoxazine XU 35610 on heating(10° C./min) in nitrogen atmosphere without additives and blends ofbenzoxazine with 10 mol % additives MgTDPA_(1:1) and MgAcTDPA.

FIG. 25 shows plots of temperature of exothermic peak maxima versusheating rate, β (° C/min). Data from DSC of benzoxazine XU 35610 withoutadditives (squares), and blends of the same benzoxazine with 10 mol %additives MgTDPA_(1:1) (MgTDPA, triangles) and MgAcTDPA (circles).

FIG. 26 shows exemplary epoxy-amine coating components:4,4′-diaminophenylsulfone and a tetrafunctional epoxy.

FIG. 27A shows an exemplary Nyquist plot of a galvanized steel couponcoated with an epoxy-amine coating containing M/MgAcTDPA after 0.5 h ofimmersion in 3.5% NaCl solution (pH 5.3) at room temperature.

FIG. 27B shows an exemplary Nyquist plot of a galvanized steel couponcoated with an epoxy-amine coating containing M/MgAcTDPA after 60 daysof immersion in 3.5% NaCl solution (pH 5.3) at room temperature.

FIG. 28 shows exemplary photographs of coated and uncoated coupons ofgalvanized steel after 60 days of immersion to 3.5% NaCl at ambienttemperature

FIG. 29 shows exemplary photographs of coupons of galvanized steelcoated with and without addition of MgAcTDPA after 30 days of immersionto 3.5% NaCl at ambient temperature.

FIG. 30 shows a plot of the release of magnesium from MgTDPA-containingpowder formulation into aqueous buffer as a function of pH. Dashed lineshows the onset of Mg(OH)₂ precipitation. Release (%)=100×(Amount of Mgin the buffer/Amount of Mg in the initial powder composition).

FIG. 31A shows SEM microphotograph of the scribe made on the galvanizedsteel panels powder-coated without (control) the corrosion inhibitorprior to the commencement of the immersion tests.

FIG. 31B shows SEM microphotograph of the scribe made on the galvanizedsteel panels powder-coated with the corrosion inhibitor (test coating)prior to the commencement of the immersion tests.

FIG. 32A shows SEM microphotograph of the scribe made on the galvanizedsteel panels powder-coated without (control) the corrosion inhibitorupon completion of the 60 days of the immersion tests. The panelsremoved from the 3.5% NaCl solutions upon completion of the test wererinsed with deionized water and gently air-dried. Arrows show edges ofthe scribes.

FIG. 32B shows SEM microphotograph of the scribe made on the galvanizedsteel panels powder-coated with the corrosion inhibitor (test coating)upon completion of the 60 days of the immersion tests. The panelsremoved from the 3.5% NaCl solutions upon completion of the test wererinsed with deionized water and gently air-dried. Arrows show edges ofthe scribes.

FIG. 33 shows exemplary results of the scribe creep measurements afterthe six-cycle test of resistance to cyclic corrosion conditions andafter 60-day immersion tests of the panels powder-coated with andwithout the corrosion inhibitor (CI), magnesium thiodipropionate(MgTDPA_(1:1)). Datapoints represent mean average scribe readings,whereas the error bars show average standard errors of the mean. Theinitial scribe widths were subtracted from the scribe creep reading.

DETAILED DESCRIPTION

Cathodic disbondment inhibitors

One aspect of the present invention is related to additive compositionsfor inhibitive coatings that prevent corrosion of metal surfaces whenapplied as primers, because such coatings are only effective ifdissolved constituents can react with the metal.^(2,3) Corrosionprotection of metal surfaces afforded by organic coatings is the mostcost-effective means of providing practical protection from corrosion intransportation and infrastructure, postponing or preventing themechanical instability, replacement expense, and safety concerns ofcorroded components. The coatings are applied to substrates subject toenvironments with a risk of atmospheric corrosion. The anticorrosivemechanism of the inhibitive coatings depends on passivation of thesubstrate and build-up of a protective barrier layer consisting ofinsoluble complexes, which impede transport of corrosive species. Theinhibitive pigments are inorganic salts, most frequently chromates,molybdates, nitrates, borates, and silicates, which are slightlywater-soluble. When the coating is permeated by moisture, the componentsof the pigments are partially dissolved and transported to the substratesurface, wherein the dissolved ions react with the substrate and form areaction product that passivates the surface of the substrate.⁴ Theinhibiting pigments should be properly distributed in the coating orprimer to maintain the integrity of the coating while partiallydissolving. The inhibitive coating should form a barrier against waterand incoming corrosive ions while releasing a sufficient quantity ofinhibitor ions. These two requirements are antagonistic and must beoptimized to enable the efficient corrosion inhibition coupled withproper barrier properties of the coating. It is clear that the effect ofthe corrosion-inhibitive coatings is to be more prominent in coatingswith some degree of permeability which, in turn, enables the masstransfer sufficient for the fractional dissolution of the pigments.

More specifically, this aspect of the present invention is related toinhibitive pigments that protect coated metal surfaces from theso-called cathodic disbondment or delamination. As defined herein,cathodic or anodic disbondment is the loss of adhesion between acathodic or anodic coating, respectively, and its metal substrate due tothe products of cathodic (anodic) redox reaction (corrosion reaction)that takes place in the interface between the coating and the metalsubstrate. Disbondment of coating occurs when said coating components ina metal interface interact either chemically or physically, causingcorrosion beneath the coat.

Cathodic disbondment or delamination is the main failure mechanism ofsteel and galvanized steel surfaces coated by organic coating layers.¹Upon permeation of water beneath the organic coating due to the passivediffusion through the coating imperfections, cracks, or metallic cutedges a corrosion cell is formed that is characterized by anodic andcathodic reactions. In other words, a cathodic disbondment mechanisminvolves the anodic metal dissolution by the electrolyte beingtransported beneath the delaminated coating, which is interlinked withthe cathodic oxygen reduction occurring at the site of the coatingdisbondment. During corrosion-driven cathodic coatingdisbondment/delamination, there occurs a cathodic O₂ reduction,primarily in the region of the delamination front:

O_(2 (g))+2H₂O+4e⁻→4OH⁻ _((aq))   (1)

The increased pH caused by reaction (1) can lead to a coatingdegradation. The corresponding anodic reaction comprises metaldissolution:

for carbon steel:

Fe_((s))→Fe²⁺ _((aq))+2e⁻  (2a)

for galvanized steel:

Zn_((s))→Zn²⁺ _((aq))+2e⁻  (2b)

The anodic metal dissolution (reactions 2a and/or 2b) is constrained tothe region of the coating defect. The anodic reaction 2b occurring atelevated pH in the disbonded regions leads to formation of water-solublezincate (ZnO₂ ²⁻) and bizincate (HZnO₂ ⁻) ions.¹

Divalent metal cations (M²⁺) inhibit the cathodic disbondment byformation of water-insoluble metal hydroxides:

[M(H₂O)₆]²⁺

[M(H₂O)₆OH]⁺+H⁺  (3)

M²⁺+2H₂O

M(OH)_(2↓)+2H⁺  (4)

Reactions (3) and (4) cause the reduction of local ion mobility andconductivity in the disbonded front underneath the coating layers andhence, to the disbondment inhibition. Rare earth (Ce³⁺, La³⁺, Gd³⁺, etc)and alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, etc.) cations are capable offorming films of amphoteric oxide layers resulting from the cathodicoxygen reduction producing alkaline pH, thus inhibiting thecorrosion-driven cathodic disbondment on bare and galvanized steelsurfaces.

Specifically, magnesium cations are preferable as divalent metal cationsas cathodic disbondment inhibitors due to abundance, low cost, non-toxicnature, and very low solubility of Mg(OH)₂ corrosion product (seereaction (4)) that forms between the hydroxyls of the cathodic oxygenreduction reaction (see (1)) and Mg²⁺ released from the coating matrixthat contains Mg²⁺. Magnesium oxides and salts exhibit a wide range ofacido-basic properties, which can be modified and tuned, and theypossess active sites capable of catalyzing numerous organic andcarbonation reactions. A wide band gap (low electron surfaceconcentration) and high stability in alkaline conditions make magnesiumhydroxide efficient in inhibiting cathodic delamination. The formationof the water-insoluble layer of Mg(OH)₂ over the substrate surfacehinders the oxygen reduction reaction and also blocks the diffusion ofother cations to the disbondment front. The cation exchange reactionsare necessary for the propagation of the disbondment front. In addition,in the case of galvanized steel, the local alkaline environment can leadto the formation of ZnO, which is an n-type semiconductor with aroom-temperature electrical conductivity, i.e., the surfaceconcentration of electrons on zinc oxide and the rate of electrontransfer are high.⁵ Conversely, formation of Mg(OH)₂ that is stableunder alkaline conditions stops the electron transfer because magnesiumhydroxide is an insulator. Hence, the corrosion inhibition effect ofMg²⁺, which has been reported to exceed the efficiency of thecommercially available, yet toxic chromate-based corrosion inhibitors.¹

Organic chelating agents as corrosion inhibitors for zinc and galvanizedmetals are known in the art.^(6,7) Furthermore, passivating compositionsfor galvanized steel and other metals composed of sulfur compounds suchas thioglycolic acids, thiodipropionic acid and the like and chromiumare known in the art.⁸ Chromium plays a specific role in thepassivation. Firstly, hydrogen ions cause zinc in the surface of thegalvanized steel substrate to dissolve into the treatment liquid, andthis acidifies (increases the hydrogen ion concentration) the surface ofthe metal to produce a chromium hydroxide. The reaction of chromium ionsand a sulfur compound produces a black metal sulfide thereon. The metalsulfide forms a black coating film that passivates the surface bysuppressing dissolution of the zinc. The utilization of chromium saltsas passivating corrosion inhibitors is problematic from the toxicitystandpoint as well as limits the applicability of the chromiumsalt/sulfur compounds due to the formation of black layers, which may beundesirable in certain applications. Disclosed herein are novel methodsof corrosion inhibition by a salt comprising a divalent alkaline earthmetal cation and an anionic thioether compound, e.g., magnesiumthiodialkanoic and the magnesium mixed salts.

Smart corrosion inhibitive polymeric pigments for organic coatings thatare ion-exchanged with magnesium are known in the art.¹ Such corrosioninhibitors comprise acid polymeric ion-exchange resin AMBERLITE™ IR120(Dow Chemical Company) loaded with Mg²⁺ by conventional ion exchange.Importantly, however, the large and strong/rubbery polymeric beads ofthe ion-exchange resin comprising said inhibitors must undergo severalelaborate processing steps to be converted into a pigment of a properparticle size: (i) first, the beads need to be thoroughly washed, then(ii) ion-exchanged via a lengthy ion-exchange process, then (iii) theloaded beads need to be dried and (iv) milled into smaller particles,which is followed by (v) sieving. It is the purpose of the presentinvention to provide a magnesium-based corrosion inhibitor wherein saidlaborious and costly processing steps are not required for the inhibitorpreparation.

The use of bentonite and more generally montmorillonite clays ascorrosion inhibitor pigments has been described.⁹ When clay isexhaustively exchanged with a divalent alkali earth and trivalent rareearth metal cation, it can constitute a smart ion-releasing pigment. Aninhibition mechanism is ion-exchanged montmorillonites may be proposedwhereby underfilm cation release and subsequent precipitation ofsparingly soluble hydroxides reduces the conductivity of the underfilmelectrolyte. This reduces the rate of corrosive disbondment. The use ofmontmorillonites is also known in the patent literature. WO2002008345 A1claims that montmorillonites are useful as corrosion inhibitors,particularly corrosion inhibitors for metallic substrates, such asgalvanized steel and the like.¹⁰ Utilization of chromate-freemontmorillonite as a corrosion inhibitor for metallic substrates allowsto alleviate the toxicity concerns prevalent with the chromate-basedcorrosion inhibitors. The compensating cationic charge present in amontmorillonite is due to one or more compensating cations selected fromalkali metal cations, alkali earth metal cations, yttrium and lanthanidecations such as cerium imbedded or intercalated into the montmorillonitesilicate structure. Clay pigments exchanged with Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺,Ce³⁺ and y³⁺ cations significantly enhance resistance tocorrosion-driven cathodic delamination in organic coatings adherent toiron surfaces.⁹ Furthermore, montmorillonite clays intercalated byorganic quaternary ammonium cations are known in the art to act ascorrosion inhibitors.¹¹ The present invention provides for clays thatare composite materials with both magnesium cations as well asthiodipropionate and the like anions, which allow for synergisticcorrosion inhibitive properties.

Organic Coating Curing Aids

Numerous curing agents for epoxides, benzoxazines and other componentsof organic coatings have been described. These curing agents includeamines, amido-amines, phenolics, carboxylic anhydrides, mercaptans, andthe like. Each curing agent has advantages and disadvantages which makeit acceptable or unsuitable for particular applications. Also, eachcuring agent, or combination thereof, may be used with one or morecuring accelerators. Examples of such accelerators include certaininorganic and organic metal salts such as lithium chloride and stannousoctoate; onium salts such as ammonium chloride, alkyl phosphoniumhalides, etc. and boron trifluoride complexes. There is a need todevelop curable epoxy and other resin compositions which cure veryrapidly at moderately elevated temperatures and have very long open time(pot life) at ambient temperatures in applications such as structuraland automotive coatings, adhesives, sheet molding compounds, primers andvarnishes.

It is the further purpose of the present invention to provide corrosionand disbondment inhibitors that promote the organic coatings preparationby accelerating curing of said coatings comprising epoxy, polyurethane,benzoxazine and the like reactive components. It was serendipitouslydiscovered that certain magnesium salts act as cathodic disbondmentinhibitors and simultaneously accelerate curing of reactive coatingcompositions by reducing temperature necessary for crosslinking and/orby Lewis acid-type catalysis.

Thioglycolic acids and their salts are known in the art. Thiodipropionicacid (TDPA) is used as antioxidant in the cosmetic industry or asintermediate in organic chemistry. TDPA esters like dilauryl-,ditridecyl-, distearyl-, and lauryl/stearyl thiodipropionates are usedin a number of polymers as antioxidants. In the presence of alcohols oramines, the carboxylic groups of TDPA will react preferentially. TDPAhas a molecular weight of 178.21 and occurs as a white crystallinepowder. It has a melting point of 131° C. to 134° C. and is soluble inwater, acetone, and alcohol. TDPA is stable under ordinary conditions.¹²

TDPA derivatives such as specific thiodipropionic acid bisamides areparticularly suitable as stabilizers for polymeric elastomers such aspolybutadiene or polyisoprene and the like which are susceptible tooxidative, thermal, light- or ozone-induced degradation.¹³ Copper saltsof TDPA derivatives can be utilized as antioxidant additives for fuelcompositions.¹⁴

Polymeric esters of TDPA with polyols, as well as containing two or morethiodipropionate groups and one or more polyol units, are known and areused as plasticizers in resins.¹⁵

Thiodipropionic acid, phenols, thiodiphenol benzoxazine, sulfonylbenzoxazine, sulfonyl and diphenol are known in the art as catalysts fortheromosetting reaction of thermal cure of benzoxazine.¹⁶ In particular,TDPA is a known catalyst of step growth ring-opening polyaddition ofbis-benzoxazine monomers that result in thermosetting polybenzoxazineresins employed in coatings. Certain thermosetting compositionscomprising TDPA as an additive exhibit improved reactivity attemperatures lower than those used during the curing of conventionalbenzoxazine based compositions. TDPA and the like thioglycolic acidderivatives such as thiol carbamates are known in the art as latentaccelerators of epoxy curing.¹⁷ Importantly, a thiodipropanoic acid andthe like compound used as accelerator of the coating cure willcovalently bind with the coating components upon cure, and hence, willnot provide for any corrosion inhibition as an undercoat. The presentinvention provides for the composition of matter that is an instrumentformed by the intermixture of a magnesium salt and thiodipropionic acidor 3,3 ′-dithiodipropionic acid and the like ingredients, and possessingserendipitous properties of accelerating the organic coatingpolymerization and curing reactions while also providing a cathodicdisbondment protection to the cured coating.

TDPA is generally recognized as a safe, nonirritating cosmetic additive.It spontaneously self-assembles into monolayers upon adsorption ontometal surfaces from aqueous solutions. The acid strength of TDPA in themonolayers is higher than that of the molecules in solutions due to theelectrostatic and coordination interactions of the carboxylic groupswith the metal surface.

Magnesium salts of thioglycolic acid are known in the art.¹⁸ By reactingin aqueous medium one mole of magnesium carbonate with two moles ofthioglycolic acid following by the removal of water by heat and/orvacuum there may be prepared a magnesium thioglycolate having thefollowing formula:

This compound may be isolated in the form of a dehydrate, which is acolorless solid material, stable in air and substantially free fromodor. Magnesium thioglycolates can be utilized as part of cosmeticformulations. However, they possess unprotected thiol groups that arestrongly reactive toward epoxy, isocyanate, amino or benzoxazolecomponents of the coatings; said reactivity results in the covalentattachment of the thiol groups onto polymeric components of the coating,thereby preventing the thioglycolate from acting as a corrosioninhibitor.

In some embodiments, a salt comprising a divalent alkaline earth metalcation and an anionic thioether compound acts as a catalyst. In someembodiments, a salt comprising a divalent alkaline earth metal cationand an anionic thioether compound acts as a crosslinking catalyst. Insome embodiments, the salt acts as a benzoxazine curing catalyst. Insome embodiments, the salt comprises a Lewis acid (metal cation) and aLewis base (organic anion). In some embodiments, the salt is abifunctional catalyst of ring-opening polymerization of benzoxazines andof the curing of oxirane-functional resins. In some embodiments, thesalt comprises hydrate water. In some embodiments, the hydrate water canparticipate in the auto-acceleration of curing via the reverse Mannichreaction and electrophilic aromatic substitution of the carbonium cationto a benzoxazine monomer or phenol. In some embodiments, the salt is amagnesium thiodipropionate.

Exemplary Compositions of Matter

Disclosed herein is a cation-releasing corrosion inhibitor comprising acarboxylate salt capable of releasing magnesium cations upondissociation. Sodium carboxylates such as salicylate, caprinate,cinnamate, decanoate or N-oleoylsarcosine, etc. are promising corrosioninhibitors on their own right in the presence of aqueous chloride ionsas a standard corrosion medium. Carboxylates can heal the local defectsin the passivating oxide layer on steel by forming weakly solubleFe(III) compounds. Remarkably, however, a synergistic effect incombining both cathodic and anodic inhibition has been realized byapplying salts of rare earths (RE) and carboxylate (HOOCR) moieties,prepared via a simple metathesis reaction (FIG. 1).

In some embodiments, the compositions disclosed herein are as effectiveas other corrosion inhibitors such as metal carboxylates. In someembodiments, the compositions disclosed herein are more effective thanother corrosion inhibitors such as metal carboxylates. In one aspect,disclosed herein is a curable coating composition comprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins.

In some embodiments, the divalent alkaline earth metal cation isselected from the group consisting of Ca²⁺, Mg²⁺, Sr²⁺, and Ba²⁺. Insome embodiments, the divalent alkaline earth metal cation is selectedfrom the group consisting of Ca²⁺ and Mg²⁺. In some embodiments, thedivalent alkaline earth metal cation is Mg²⁺.

In contrast to magnesium thioglycolates, magnesium thiodialkanoic acidsalts, dithiodialkanonic acid salts and the like compounds (FIG. 2)containing sulfane sulfur (thioether) in place of thiol —SH group aredevoid of the active sulfur hydrogen and hence, will not covalently bindsulfur-containing groups to the reactive components of the organiccoatings. Magnesium thiodialkanoate or dithiodialkanonate and the likesalt embedded into a cured polymer organic coating is available fordissociating on contact with water, thus freeing magnesium cations, Mg²⁺to the immediate proximity. Such salts can optionally be mixed saltsthat contain both thiodialkanoate and the like anions as well as anionsoriginating from commonly available magnesium salts such as acetate,nitrate, chloride, sulfate and the like. Said magnesium thiodialkanoateor dithiodialkanonate salts can contain hydrate water in variousproportions.

In some embodiments of the compositions disclosed herein, the anionicthioether compound is a thioalkanoic acid or a dithioalkanoic acid. Insome embodiments, the anionic thioether compound is a thioalkanoic acid.

In some embodiments of the compositions disclosed herein, the salt hasthe following structural formula:

wherein

R is selected from the group consisting of divalent (C₁-C₆)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,and (C₂-C₆)alkenyl;

R¹ is selected from the group consisting of divalent (C₁-C₆)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,and (C₂-C₆)alkenyl;

R² is hydrogen or (C₁-C₂o)alkyl; and

X is selected from the group consisting of H, halogen, (C₁-C₂₀)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,(C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂, —C(O)N(R²)₂,—C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R².

In some embodiments, the salt is selected from the group consisting of

(FIG. 2). In some embodiments, the

salt is

In some embodiments, the thioalkanoic acid is selected from the groupconsisting of thiodipropionic acid (TDPA), lauryl thiodipropionate,tridecyl thiodipropionate, stearyl thiodipropionate, and myristoylthiodipropionate.

In some embodiments, the anionic thioether compound is a dithioalkanoicacid.

In some embodiments of the compositions disclosed herein, the salt hasthe following structural formula:

wherein

R is selected from the group consisting of divalent (C₁-C₆)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,and (C₂-C₆)alkenyl;

R¹ is selected from the group consisting of divalent (C₁-C₆)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,and (C₂-C₆)alkenyl;

R² is hydrogen or (C₁-C₂₀)alkyl;

X is selected from the group consisting of absent, H, halogen,(C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂, —C(O)N(R²)₂,—C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R²; and

n is 1 or 2.

In some embodiments of formulas (I) and (II) disclosed herein, R isselected from the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl,aryl, aralkyl, and (C₂-C₆)alkenyl. In some embodiments, R is selectedfrom the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl,heterocycloalkyl, and (C₂-C₆)alkenyl. In some embodiments, R is selectedfrom the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl, aryl,aralkyl, and (C₂-C₆)alkenyl. In some embodiments, R is selected from thegroup consisting of divalent (C₁-C₆)alkyl, cycloalkyl and aryl. In someembodiments, R is (C₁-C₆)alkyl or aryl. In some embodiments, R is(C₁-C₆)alkyl.

In some embodiments of formulas (I) and (II) disclosed herein, R¹ isselected from the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl,aryl, aralkyl, and (C₂-C₆)alkenyl. In some embodiments, R¹ is selectedfrom the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl,heterocycloalkyl, and (C₂-C₆)alkenyl. In some embodiments, R¹ isselected from the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl,aryl, aralkyl, and (C₂-C₆)alkenyl. In some embodiments, R¹ is selectedfrom the group consisting of divalent (C₁-C₆)alkyl, cycloalkyl and aryl.In some embodiments, R¹ is (C₁-C₆)alkyl or aryl. In some embodiments, R¹is (C₁-C₆)alkyl.

In some embodiments, R and R¹ are the same. In some embodiments, R andR¹ are both (C₁-C₆)alkyl. In some embodiments, R and R¹ are both aryl.

In some embodiments of formulas (I) and (II) disclosed herein, X isselected from the group consisting of absent, H, halogen, (C₁-C₂₀)alkyl,cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, heteroaralkyl,(C₂-C₂₀)alkenyl, —C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and—C(O)R². In some embodiments, X is selected from the group consisting ofabsent, H, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, and —C(O)R². Insome embodiments, X is selected from the group consisting of absent, H,(C₁-C₂₀)alkyl, aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, and —C(O)R². Insome embodiments, X is selected from the group consisting of absent, H,(C₁-C₂₀)alkyl, (C₂-C₂₀)alkenyl, and —C(O)R². In some embodiments, X isselected from the group consisting of H, (C₁-C₂₀)alkyl, and —C(O)R². Insome embodiments, X is absent.

In some embodiments, R² is hydrogen. In some embodiments, X is —C(O)R²;and R² is (C₁-C₂₀)alkyl.

In some embodiments, n is 1. In some embodiments, n is 2.

In some embodiments, the salt is selected from the group consisting of

In some embodiments, the salt is

In some embodiments, the dithioalkanoic acid is selected from the groupconsisting of 3,3′-thiodipropionic acid, lauryl dithiodipropionate,tridecyl dithiodipropionate, stearyl dithiodipropionate, and myristoyldithiodipropionate.

In some embodiments, the ratio of the divalent alkaline earth metalcation to the anionic thioether compound is from about 50:1 to about0.01:1. In some embodiments, the ratio is about 50:1 to about 0.1:1. Insome embodiments, the ratio of the divalent alkaline earth metal cationto the anionic thioether compound is selected from the group consistingof about 50:1, about 49:1, about 48:1, about 47:1, about 46:1, about45:1, about 44:1, about 43:1, about 42:1, about 41:1, about 40:1, about39:1, about 38:1, about 37:1, about 36:1, about 35:1, about 34:1, about33:1, about 32:1, about 31:1, about 30:1, about 29:1, about 28:1, about27:1, about 26:1, about 25:1, about 24:1, about 23:1, about 22:1, about21:1, about 20:1, about 19:1, about 18:1, about 17:1, about 16:1, about15:1, about 14:1, about 13:1, about 12:1, about 11:1, about 10:1, about9:1, about 8:1, about 7:1, about 6:1, about 5.9:1, about 5.8:1, about5.7:1, about 5.6:1, about 5.5:1, about 5.4:1, about 5.3:1, about 5.2:1,about 5.1:1, about 5:1, about 4.9:1, about 4.8:1, about 4.7:1, about4.6:1, about 4.5:1, about 4.4:1, about 4.3:1, about 4.2:1, about 4.1:1,about 4:1, about 3.9:1, about 3.8:1, about 3.7:1, about 3.6:1, about3.5:1, about 3.4:1, about 3.3:1, about 3.2:1, about 3.1:1, about 3:1,about 2.9:1, about 2.8:1, about 2.7:1, about 2.6:1, about 2.5:1, about2.4:1, about 2.3:1, about 2.2:1, about 2.1:1, about 2:1, about 1.9:1,about 1.8:1, about 1.7:1, about 1.6:1, about 1.5:1, about 1.4:1, about1.3:1, about 1.2:1, about 1.1:1, about 1:1, about 0.9:1, about 0.8:1,about 0.7:1, about 0.6:1, about 0.5:1, about 0.4:1, about 0.3:1, about0.2:1, and about 0.1:1. In some embodiments, the ratio of the divalentalkaline earth metal cation to the anionic thioether compound is fromabout 25:1 to about 0.1:1. In some embodiments, the ratio of thedivalent alkaline earth metal cation to the anionic thioether compoundis from about 10:1 to about 0.5:1. In some embodiments, the ratio of thedivalent alkaline earth metal cation to the anionic thioether compoundis from about 5:1 to about 0.5:1.

In some embodiments of the salts disclosed herein, the salt is preparedvia an aqueous route. In some embodiments, the salt is prepared using ametathesis reaction (see, for example, FIG. 1). In some embodiments, thesalt is prepared using a substitution reaction (see, for example, FIG.3).

Methods of application of magnesium salts of thiodialkanoic ordithioalkanoic acids and the like compounds as latent accelerators ofresin curing has been serendipitously discovered as disclosed in thepresent invention. In some embodiments, the salt comprising a divalentalkaline earth metal cation and an anionic thioether compound is acuring agent. Therefore, in some embodiments, the requirements ofcomponents (a) and (b) of the curable coating composition are met by asalt comprising a divalent alkaline earth metal cation and an anionicthioether compound.

In some embodiments, the curing agent or the mixture of curing agentscomprises an amine, an amido-amine, a phenol, a carboxylic anhydride, ora mercaptan.

In some embodiments, the salt comprising a divalent alkaline earth metalcation and an anionic thioether compound further comprises a secondanionic compound. In some embodiments, the second anionic compound isselected from the group consisting of acetate, nitrate, chloride, andsulfate. In some embodiments, the salt is magnesium acetatethiodipropionate mixed salt. In some embodiments, the salt is magnesiumacetate dithiodipropionate mixed salt.

In some embodiments of the compositions disclosed herein, the salt isfrom about 0.1% to about 80% by weight, based upon total solids weightof the composition. In some embodiments, the salt is from about 0.1% toabout 65% by weight, based upon total solids weight of the composition.In some embodiments, the weight of the salt, based upon total solidsweight of the composition, is selected from the group consisting ofabout 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%,about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.1%, about 1.2%,about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%,about 1.9%, about 2%, about 2.1%, about 2.2%, about 2.3%, about 2.4%,about 2.5%, about 2.6%, about 2.7%, about 2.8%, about 2.9%, about 3%,about 3.1%, about 3.2%, about 3.3%, about 3.4%, about 3.5%, about 3.6%,about 3.7%, about 3.8%, about 3.9%, about 4%, about 4.1%, about 4.2%,about 4.3%, about 4.4%, about 4.5%, about 4.6%, about 4.7%, about 4.8%,about 4.9%, about 5%, about 5.1%, about 5.2%, about 5.3%, about 5.4%,about 5.5%, about 5.6%, about 5.7%, about 5.8%, about 5.9%, about 6%,about 6.1%, about 6.2%, about 6.3%, about 6.4%, about 6.5%, about 6.6%,about 6.7%, about 6.8%, about 6.9%, about 7%, about 7.1%, about 7.2%,about 7.3%, about 7.4%, about 7.5%, about 7.6%, about 7.7%, about 7.8%,about 7.9%, about 8%, about 8.1%, about 8.2%, about 8.3%, about 8.4%,about 8.5%, about 8.6%, about 8.7%, about 8.8%, about 8.9%, about 9%,about 9.1%, about 9.2%, about 9.3%, about 9.4%, about 9.5%, about 9.6%,about 9.7%, about 9.8%, about 9.9%, about 10%, about 10.1%, about 10.2%,about 10.3%, about 10.4%, about 10.5%, about 10.6%, about 10.7%, about10.8%, about 10.9%, about 11%, about 12%, about 13%, about 14%, about15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%,about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%,about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%,about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%,about 61%, about 62%, about 63%, about 64%, and about 65%. In someembodiments, the salt is from about 0.1% to about 50% by weight, basedupon total solids weight of the composition. In some embodiments, thesalt is from about 5% to about 50% by weight, based upon total solidsweight of the composition.

In some embodiments of the compositions disclosed herein, the curableorganic resin comprises an epoxy, an amine, a polyamidoamine, apolyurethane, a benzoxazine, or a mixture thereof. In some embodiments,the curable organic resin comprises an epoxy. In some embodiments, thecurable organic resin comprises an epoxy and an amine. In someembodiments, the curable organic resin comprises a bisphenol A epoxyresin, bisphenol A propoxylate diglycidyl ether, orN⁴,N⁴,N⁴′,N⁴′-tetra(oxiran-2-yl)-[1,1′-biphenyl]-4,4′-diamine. In someembodiments, the curable organic resin comprises bisphenol A epoxy resin(60-100%), glycidylether of C₁₂-C₁₄ alcohols (7-13%), and butylphenylglycidyl ether (3-7%).

In some embodiments, the curable organic resin comprises an amine. Insome embodiments, the curable organic resin comprises an amine selectedfrom the group consisting of 4,4′-diaminophenylsulfone,diethylenetriamine, polyoxypropylene diamine, triethanolamine, and2-(2-aminoethylamino)ethanol. In some embodiments, the curable organicresin comprises diethylenetriamine (13-30%), polyoxypropylene diamine(13-30%), 4-nonyl-phenol (7-13%), triethanolamine (3-7%), and2-(2-aminoethylamino)ethanol (0.1-1%).

In some embodiments, the curable organic resin comprises4,4′-diaminophenylsulfone.

In some embodiments, the curable organic resin comprises apolyamidoamine. In some embodiments, the polyamidoamine is ARADUR® 125BDB.

In some embodiments, the compositions disclosed herein further comprise:

-   -   a pigment; or    -   an additive.

In some embodiments, in the composition comprises a pigment. In someembodiments, the pigment is selected from the group consisting of carbonnanotubes, titanium dioxide, montmorillonite, iron oxide, aluminum,bronze, phthalocyanine blue, and a mixture thereof. In some embodiments,the pigment is montmorillonite. In some embodiments, the pigment isMontmorillonite K 10 clay.

Furthermore, the compositions of matter may comprise composites of saidmagnesium salts and clays such as preferably bentonite, a form of moregenerally montmorillonite, 2:1-layer hydrated aluminium silicates basedon the dioctahedral pyrophyllite structure.

In some embodiments of the compositions of matter disclosed herein, thecomposition comprises magnesium acetate thiodipropionate mixed salt anda pigment. In some embodiments, the composition comprises a blend ofmontmorillonites and a salt comprising a divalent alkaline earth metalcation and an anionic thioether compound. In some embodiments, thecomposition comprises a composite of montmorillonites and a saltcomprising a divalent alkaline earth metal cation and an anionicthioether compound.

In some embodiments of the compositions disclosed herein, thecomposition comprises an additive. In some embodiments, the compositionsdisclosed herein further comprise an additive.

In some embodiments, the additive is selected from the group consistingof a dye, a flow control agent, a dispersant, a thixotropic agent, anadhesion promoter, an antioxidant, a light stabilizer, a curingcatalyst, an anticorrosion agent, and a mixture thereof. In someembodiments, the additive is carbon nanotubes.

In some embodiments, the composition comprises the salt magnesiumacetate thiodipropionate; and the curing agent 4,4′-diaminophenylsulfone.

Exemplary Methods of Use

In another aspect, provided herein are methods of anticorrosivetreatments comprising coating a substrate or an article with any one ofthe compositions disclosed herein. In some embodiments, a method ofanticorrosive treatment comprises:

providing a substrate, wherein said substrate is a ferrous substrate;coating the substrate with a composition comprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins;        thereby preventing or reducing corrosion of the substrate.

In another aspect, provided herein are methods of preventing or reducingcorrosion on a surface comprising coating a substrate or an article withany one of the compositions disclosed herein. In some embodiments, amethod of preventing or reducing corrosion on a surface, comprisingapplying to the surface a coating, comprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins;        thereby preventing or reducing corrosion of the surface.

In some embodiments, the salts disclosed herein can act synergisticallyas corrosion inhibitors and as curing agents. In some embodiments,magnesium thiodipropionates can act synergistically as corrosioninhibitors, which lower the temperature of the epoxy-amine gelation andbenzoxazine curing.

In some embodiments, the salts disclosed herein significantly improve anepoxy-amine powder coating resistance to cathodic disbondment ongalvanized steel in industry-standard cyclic tests.

In some embodiments, the surface is a surface of a substrate.

In some embodiments, the substrate is selected from the group consistingof silicon wafer, glass slide, quartz, poly(ethylene terephthalate)(PET) roll, MELINEX®, polyethylenenaphtalate (PEN) roll, TEONEX®, kaptonroll, paper roll, polydimethylsiloxane roll, nylon, polyester,polyurethane, polyanhydride, polyorthoester, polyacrylonitrile,polyphenazine, latex, teflon, dacron, acrylate polymer, chlorinatedrubber, fluoropolymer, polyamide resin, vinyl resin, GORE-TEX®, MARLEX®,expanded polytetrafluoroethylene (e-PTFE), low density polyethylene(LDPE), high density polyethylene (HDPE), polyimide (PI), polypropylene(PP), steel, carbon steel, galvanized steel, and pig iron. In someembodiments, the substrate is selected from the group consisting ofsilicon wafer, glass slide, quartz, polyurethane, polyacrylonitrile,polyphenazine, teflon, polyamide resin, GORE-TEX®, MARLEX®, expandedpolytetrafluoroethylene (e-PTFE), polyimide (PI), steel, carbon steel,galvanized steel, and pig iron. In some embodiments, the substrate isselected from the group consisting of steel, carbon steel, galvanizedsteel, and pig iron.

In some embodiments of the methods disclosed herein, a passivation layeris formed on the substrate.

In some embodiments of the methods disclosed herein, at least a portionof the substrate is in contact with water.

In some embodiments of the methods disclosed herein, the method forms agel within a curing time. In some embodiments, the curing time is lessthan 60 minutes, less than 55 minutes, less than 50 minutes, less than45 minutes, less than 40 minutes, less than 35 minutes, less than 30minutes, less than 25 minutes, less than 20 minutes, less than 19minutes, less than 18 minutes, less than 17 minutes, less than 16minutes, less than 15 minutes, less than 14 minutes, less than 13minutes, less than 12 minutes, less than 11 minutes, less than 10minutes, less than 9 minutes, less than 8 minutes, less than 7 minutes,less than 6 minutes, less than 5 minutes, less than 4 minutes, less than3 minutes, less than 2 minutes, less than 1 minute, and less than 30seconds. In some embodiments, the curing time is less than about 10minutes. In some embodiments, the curing time is less than about 8minutes. In some embodiments, the curing time is less than about 5minutes. In some embodiments, the curing time is selected from the groupconsisting of about 15 seconds, about 30 seconds, about 45 seconds,about 1 minute, about 1.25 minutes, about 1.5 minutes, about 1.75minutes, about 2 minutes, about 2.25 minutes, about 2.5 minutes, about2.75 minutes, about 3 minutes, about 3.25 minutes, about 3.5 minutes,about 3.75 minutes, about 4 minutes, about 4.25 minutes, about 4.5minutes, about 4.75 minutes, about 5 minutes, about 5.25 minutes, about5.5 minutes, about 5.75 minutes, about 6 minutes, about 6.25 minutes,about 6.5 minutes, about 6.75 minutes, about 7 minutes, about 7.25minutes, about 7.5 minutes, about 7.75 minutes, about 8 minutes, about8.25 minutes, about 8.5 minutes, about 8.75 minutes, about 9 minutes,about 9.25 minutes, about 9.5 minutes, about 9.75 minutes, and about 10minutes.

In some embodiments of the methods disclosed herein, the curing agent orthe mixture of curing agents is a thermoset monomer.

In some embodiments, the thermoset monomer shows an onset of curing at atemperature as measured using differential scanning calorimetry. In someembodiments, the onset temperature is less than 225° C. In someembodiments, the onset temperature is less than 200° C. In someembodiments, the onset temperature is selected from the group consistingof less than 200° C., less than 195° C., less than 190° C., less than185° C., less than 180° C., less than 175° C., less than 170° C., lessthan 165° C., less than 160° C., less than 155° C., less than 150° C.,less than 145° C., less than 140° C., less than 135° C., less than 130°C., less than 125° C., less than 120° C., less than 115° C., less than110° C., less than 105° C., and less than 100° C. In some embodiments,the onset temperature is less than 175° C. In some embodiments, theonset temperature is less than 150° C. In some embodiments, the onsettemperature is less than 125° C. In some embodiments, the onsettemperature is less than 100° C.

In some embodiments, the onset temperature is selected from the groupconsisting of about 200° C., about 199° C., about 198° C., about 197°C., about 196° C., about 195° C., about 194° C., about 193° C., about192° C., about 191° C., about 190° C., about 189° C., about 188° C.,about 187° C., about 186° C., about 185° C., about 184° C., about 183°C., about 182° C., about 181° C., about 180° C., about 179° C., about178° C., about 177° C., about 176° C., about 175° C., about 174° C.,about 173° C., about 172° C., about 171° C., about 170° C., about 169°C., about 168° C., about 167° C., about 166° C., about 165° C., about164° C., about 163° C., about 162° C., about 161° C., about 160° C.,about 159° C., about 158° C., about 157° C., about 156° C., about 155°C., about 154° C., about 153° C., about 152° C., about 151° C., about150° C., about 149° C., about 148° C., about 147° C., about 146° C.,about 145° C., about 144° C., about 143° C., about 142° C., about 141°C., about 140° C., about 139° C., about 138° C., about 137° C., about136° C., about 135° C., about 134° C., about 133° C., about 132° C.,about 131° C., about 130° C., about 129° C., about 128° C., about 127°C., about 126° C., about 125° C., about 124° C., about 123° C., about122° C., about 121° C., about 120° C., about 119° C., about 118° C.,about 117° C., about 116° C., about 115° C., about 114° C., about 113°C., about 112° C., about 111° C., about 110° C., about 109° C., about108° C., about 107° C., about 106° C., about 105° C., about 104° C.,about 103° C., about 102° C., about 101° C., and about 100° C.

Devices

In another aspect, provided herein is an article, comprising asubstrate, and a coating on the substrate, wherein the coating comprisesa composition comprising:

-   -   (a) a salt comprising a divalent alkaline earth metal cation and        an anionic thioether compound;    -   (b) a curing agent or a mixture of curing agents; and    -   (c) one or more curable organic resins.

In some embodiments of the article, the article comprises steel, carbonsteel, galvanized steel, or pig iron. In some embodiments, the article,included but is not limited to, an electrode, a vehicle (e.g., a car, aboat, a truck, a four-wheeler, and a piece of farming equipment), abuilding component (e.g., a fence, a metal bar, a grate, and a metalbeam), a weapon (e.g., a gun, a knife, a sword, and a spear), abarricade, and a sign (e.g., a road sign). In some embodiments, thearticle is an electrode. In some embodiments, the article is a vehicle.

Definitions

For convenience, certain terms employed in the specification, examples,and are conjunctively present in some cases and disjunctively present inother cases. Multiple elements listed with “and/or” should be construedin the same fashion, i.e., “one or more” of the elements so conjoined.Other elements may optionally be present other than the elementsspecifically identified by the “and/or” clause, whether related orunrelated to those elements specifically identified. Thus, as anon-limiting example, a reference to “A and/or B”, when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A only (optionally including elements other than B);in another embodiment, to B only (optionally including elements otherthan A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e., “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

For purposes of this disclosure, the chemical elements are identified inaccordance with the Periodic Table of the Elements, CAS version,Handbook of Chemistry and Physics, 67th Ed., 1986-87, inside cover.

As used herein, the term “surface” or “surfaces” or “substrates” canmean any surface of any material, including glass, plastics, metals,polymers, paper, fabric and the like. It can include surfacesconstructed out of more than one material, including coated surfaces.Importantly, all surfaces/substrates of the disclosure can be coatedwith the compositions of the disclosure, resulting in improved corrosionprotection.

An aliphatic chain comprises the classes of alkyl, alkenyl and alkynyldefined below. A straight aliphatic chain is limited to unbranchedcarbon chain moieties. As used herein, the term “aliphatic group” refersto a straight chain, branched-chain, or cyclic aliphatic hydrocarbongroup and includes saturated and unsaturated aliphatic groups, such asan alkyl group, an alkenyl group, or an alkynyl group.

“Alkyl” refers to a fully saturated cyclic or acyclic, branched orunbranched carbon chain moiety having the number of carbon atomsspecified, or up to 30 carbon atoms if no specification is made. Forexample, alkyl of 1 to 8 carbon atoms refers to moieties such as methyl,ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl, and thosemoieties which are positional isomers of these moieties. Alkyl of 10 to30 carbon atoms includes decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl,heneicosyl, docosyl, tricosyl and tetracosyl. In certain embodiments, astraight chain or branched chain alkyl has 30 or fewer carbon atoms inits backbone (e.g., C₁-C₃₀ for straight chains, C₃-C₃₀ for branchedchains), and more preferably 20 or fewer.

“Cycloalkyl” means mono- or bicyclic or bridged saturated carbocyclicrings, each having from 3 to 12 carbon atoms. Likewise, preferredcycloalkyls have from 5-12 carbon atoms in their ring structure, andmore preferably have 6-10 carbons in the ring structure.

“Alkenyl” refers to any cyclic or acyclic, branched or unbranchedunsaturated carbon chain moiety having the number of carbon atomsspecified, or up to 26 carbon atoms if no limitation on the number ofcarbon atoms is specified; and having one or more double bonds in themoiety. Alkenyl of 6 to 26 carbon atoms is exemplified by hexenyl,heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodenyl, tridecenyl,tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl,nonadecenyl, eicosenyl, heneicosoenyl, docosenyl, tricosenyl, andtetracosenyl, in their various isomeric forms, where the unsaturatedbond(s) can be located anywherein the moiety and can have either the (Z)or the (E) configuration about the double bond(s).

The terms “alkoxyl” or “alkoxy” as used herein refers to an alkyl group,as defined below, having an oxygen moiety attached thereto.Representative alkoxyl groups include methoxy, ethoxy, propoxy,tert-butoxy, and the like. An “ether” is two hydrocarbons covalentlylinked by an oxygen. Accordingly, the substituent of an alkyl thatrenders that alkyl an ether is or resembles an alkoxyl, such as can berepresented by one of —O-alkyl, —O-alkenyl, —O-alkynyl, —O—(CH₂)_(m)—R¹,where m and R₁ are described below.

The terms “amine” and “amino” are art-recognized and refer to bothunsubstituted and substituted amines, e.g., a moiety that can berepresented by the formulae:

wherein R³, R⁵ and R⁶ each independently represent a hydrogen, an alkyl,an alkenyl, —(CH₂)_(m)—R¹, or R³ and R⁵ taken together with the N atomto which they are attached complete a heterocycle having from 4 to 8atoms in the ring structure; R¹ represents an alkenyl, aryl, cycloalkyl,a cycloalkenyl, a heterocyclyl, or a polycyclyl; and m is zero or aninteger in the range of 1 to 8. In certain embodiments, only one of R³or R⁵ can be a carbonyl, e.g., R³, R⁵, and the nitrogen together do notform an imide. In even more certain embodiments, R³ and R⁵ (andoptionally R⁶) each independently represent a hydrogen, an alkyl, analkenyl, or —(CH₂)_(m)—R¹. Thus, the term “alkylamine” as used hereinmeans an amine group, as defined above, having a substituted orunsubstituted alkyl attached thereto, i.e., at least one of R3 and R5 isan alkyl group. In certain embodiments, an amino group or an alkylamineis basic, meaning it has a conjugate acid with a pK_(a)≥7.00, i.e., theprotonated forms of these functional groups have pK_(a)s relative towater above about 7.00.

The term “aryl” as used herein includes 3- to 12-membered substituted orunsubstituted single-ring aromatic groups in which each atom of the ringis carbon (i.e., carbocyclic aryl) or where one or more atoms areheteroatoms (i.e., heteroaryl). Preferably, aryl groups include 5- to12-membered rings, more preferably 6- to 10-membered rings. In certainembodiments, aryl includes (C₆-C₁₀)aryl. The term “aryl” also includespolycyclic ring systems having two or more cyclic rings in which two ormore carbons are common to two adjoining rings wherein at least one ofthe rings is aromatic, e.g., the other cyclic rings can be cycloalkyls,cycloalkenyls, cycloalkynyls, aryls, heteroaryls, and/or heterocyclyls.Carbocyclic aryl groups include benzene, naphthalene, phenanthrene,phenol, aniline, and the like. Heteroaryl groups include substituted orunsubstituted aromatic 3- to 12-membered ring structures, morepreferably 5- to 12-membered rings, more preferably 6- to 10-memberedrings, whose ring structures include one to four heteroatoms. In certainembodiments, heteroaryl includes (C₂-C₉)heteroaryl. Heteroaryl groupsinclude, for example, pyrrole, furan, thiophene, imidazole, oxazole,thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine andpyrimidine, and the like.

The term “aralkyl” is art-recognized and refers to an alkyl groupsubstituted with an aryl group.

The term “heteroaralkyl” is art-recognized and refers to an alkyl groupsubstituted with a heteroaryl group.

The term “heteroatom” is art-recognized and refers to an atom of anyelement other than carbon or hydrogen. Illustrative heteroatoms includeboron, nitrogen, oxygen, phosphorus, sulfur and selenium.

The terms “heterocyclyl”, “heterocycloalkyl”, “heterocyclic group” referto 3- to 12-membered ring structures, more preferably 5- to 12-memberedrings, more preferably 6- to 10-membered rings, whose ring structuresinclude one to four heteroatoms. Heterocycles can also be polycycles. Incertain embodiments, heterocyclyl includes (C₂-C₉)heterocyclyl.Heterocyclyl groups include, for example, thiophene, thianthrene, furan,pyran, isobenzofuran, chromene, xanthene, phenoxathiin, pyrrole,imidazole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine,pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine,quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine,quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline,phenanthridine, acridine, pyrimidine, phenanthroline, phenazine,phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane,thiolane, oxazole, piperidine, piperazine, morpholine, lactones, lactamssuch as azetidinones and pyrrolidinones, sultams, sultones, and thelike. The heterocyclic ring can be substituted at one or more positionswith such substituents as described above, as for example, halogen,alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, amino, nitro,sulfhydryl, imino, amido, phosphate, phosphonate, phosphinate, carbonyl,carboxyl, silyl, sulfamoyl, sulfinyl, ether, alkylthio, sulfonyl,ketone, aldehyde, ester, a heterocyclyl, an aromatic or heteroaromaticmoiety, —CF₃, —CN, and the like.

The term “carbonyl” is art-recognized and includes such moieties as canbe represented by the formula:

wherein X is a bond or represents an oxygen or a sulfur, and R⁷represents a hydrogen, an alkyl, an alkenyl, —(CH₂)_(m)—R¹ or apharmaceutically acceptable salt, R⁸ represents a hydrogen, an alkyl, analkenyl or —(CH₂)_(m)—R¹, where m and R¹ are as defined above. Where Xis an oxygen and R⁷ or R⁸ is not hydrogen, the formula represents an“ester.” Where X is an oxygen, and R⁷ is as defined above, the moiety isreferred to herein as a carboxyl group, and particularly when R⁷ is ahydrogen, the formula represents a “carboxylic acid”. Where X is anoxygen, and R⁸ is a hydrogen, the formula represents a “formate.” Ingeneral, where the oxygen atom of the above formula is replaced by asulfur, the formula represents a “thiocarbonyl” group. Where X is asulfur and R⁷ or R⁸ is not hydrogen, the formula represents a“thioester” group. Where X is a sulfur and R⁷ is a hydrogen, the formularepresents a “thiocarboxylic acid” group. Where X is a sulfur and R⁸ isa hydrogen, the formula represents a “thioformate” group. On the otherhand, where X is a bond, and R⁷ is not hydrogen, the above formularepresents a “ketone” group. Where X is a bond, and R⁷ is a hydrogen,the above formula represents an “aldehyde” group.

As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and nonaromaticsubstituents of organic compounds. Illustrative substituents include,for example, those described herein above. The permissible substituentscan be one or more and the same or different for appropriate organiccompounds. For purposes of this invention, the heteroatoms such asnitrogen may have hydrogen substituents and/or any permissiblesubstituents of organic compounds described herein which satisfy thevalences of the heteroatoms. This invention is not intended to belimited in any manner by the permissible substituents of organiccompounds. It will be understood that “substitution” or “substitutedwith” includes the implicit proviso that such substitution is inaccordance with permitted valence of the substituted atom and thesubstituent, and that the substitution results in a stable compound,e.g., which does not spontaneously undergo transformation such as byrearrangement, cyclization, elimination, etc.

As used herein, the term “halogen” designates —F, —Cl, —Br, or —I; theterm “thioether” means —S—; and the term “hydroxyl” means —OH.

The abbreviations Ac, Me, Et, Ph, Tf, Nf, Ts, and Ms represent acetate,methyl, ethyl, phenyl, trifluoromethanesulfonyl,nonafluorobutanesulfonyl, p-toluenesulfonyl and methanesulfonyl,respectively. A more comprehensive list of the abbreviations utilized byorganic chemists of ordinary skill in the art appears in the first issueof each volume of the Journal of Organic Chemistry; this list istypically presented in a table entitled Standard List of Abbreviations.

TDPA is an abbreviation for 3,3′-thiodipropionic acid.

DTDPA is an abbreviation for 3,3′-dithiodipropionic acid.

MgAc is an abbreviation for magnesium acetate tetrahydrate.

MgAcTDPA is an abbreviation for magnesium acetate thiodipropionate.

M/MgAcTDPA is an abbreviation for composites of montmorillonite withmagnesium acetate thiodipropionate.

EXAMPLES Example 1 Materials

Metallic magnesium powder (≥99%, mesh 325), magnesium acetatetetrahydrate (≥99%), magnesium nitrate hexahydrate (99%),3,3′-thiodipropionic acid (TDPA, 97%), dicyandiamide (99%), andmontmorillonite K10 were all obtained from Sigma Aldrich Chemical Co.and used as received. Benzoxazine resin (product designation, XU35610),ARALDITE® GT 6259 resin (bisphenol A based epoxy resin modified with anepoxy cresol novolac) and two-part curing system comprisingARALDITE®LY8601 resin and ARADUR® 8602 hardener were supplied byHuntsman Advanced Materials, Inc. (Woodlands, Tex.). ARALDITE® LY8601 iscomposed of bisphenol A epoxy resin (60-100%), glycidylether of C₁₂-C₁₄alcohols (7-13%), and butylphenyl glycidyl ether (3-7%), whereas ARADUR®8602 is composed principally of diethylenetriamine (13-30%),polyoxypropylene diamine (13-30%), 4-nonyl-phenol (7-13%),triethanolamine (3-7%), and 2-(2-aminoethylamino)ethanol (0.1-1%).Carbon black (Emperor 1600) was obtained from Cabot Corp. (Billerica,Mass.). All other chemicals, solvents and buffers were obtained fromcommercial sources and were of the highest purity available.

Syntheses

A sample of Mg(OH)₂ was prepared by precipitating it from an aqueoussolution of magnesium nitrate by an ammonium hydroxide solution at pH10-11. The precipitate was purified by centrifugation and resuspensioncycles with deionized water, then dried at 100° C. and stored as apowder.

General Methods ¹H NMR spectra were taken at 400 MHz using a BrukerAvance 400 spectrometer. FTIR measurements were conducted using aNicolet 8700 FTIR spectrometer and a Specac Smart Golden Gate AttenuatedTotal Reflection Accessory (ATR). Spectra of the powderous materialswere measured in KBr tablets at 1 cm⁻¹ resolution with 64 scans, whereaselectrode surfaces were subjected to ATR. A total of 128 spectra (2 cm⁻¹resolution) were acquired and averaged for every sample. X-raydiffraction (XRD) spectra were acquired at room temperature for 6 heach, using an X'Pert Panalytical Pro diffractometer equipped with anX'celerator high-speed detector coupled with a Ni β-filter. Source ofX-rays was Cu K-α (wavelength 1.540598 Å).

Programmable divergence slits were used to illuminate a constant lengthof the samples (4 mm), with 0.02 soller slits. The XRD analysis for wasperformed using the Treor indexing method.¹⁹ The maximum cell volume wasset to less than 1500 A³, and both Pawley and mixed profile fits wereused to narrow down the space group and predicted peak intensities. Amanual range of peaks from 5 to 45° was used to perform the analysis,with the first 25 peaks used to carry out the fit. Thermogravimetricanalysis (TGA) and simultaneous differential scanning calorimetry (DSC)were conducted using a Q600 TGA/DSC instrument (TA Instruments, Inc.,New Castle, Del.). Samples were subjected to heating scans (10° C./min)under nitrogen atmosphere in a temperature ramp mode.

Analysis of the magnesium thiodipropionate surface was performed with aPhysical Electronics Versaproble II X-ray photoelectron spectrometer(XPS). The analysis was performed at ultrahigh vacuum (1×10⁻⁸ bar) withan argon-gun neutralizer. The survey scans were performed with 10 cyclesfrom 1400 to 50 eV at 200 kV with a pass energy of 80 eV and a step sizeof 0.5 eV. The high-resolution scans were performed at 100 kV, a passenergy of 11 eV, and 0.05 eV resolution with 30 cycles for iron and 8cycles for the remaining elements. The surface morphology of thematerials was characterized by a FEG-XL-30 field-emission SEM at 20 kVusing a beam size of 3 and high-vacuum conditions, and a ZEISS MerlinHigh-Resolution SEM at 15 kV under high vacuum.

Synthesis and Properties of an Exemplary Thioether Salt

A. Synthesis

A mixed salt of magnesium acetate and thiodipropionic acid (magnesiumacetate thiodipropionate, MgAcTDPA) was prepared as follows. Magnesiumacetate tetrahydrate (Sigma Aldrich, 99%, 2.14 g, 1 mmol) andthiodipropionic acid (Sigma Aldrich, 98%, 1.78 g, 1 mmol) were dissolvedin deionized water (50 mL) and the solution was evaporated on air at 60°C. for 16 h, resulting in a transparent glassy solid. The product wasredissolved in 50 mL deionized water and the solution was snap-frozen inliquid nitrogen and lyophilized to dryness for 5 days at 10 mTorr vacuumresulting in glassy snow-like whitish to transparent crystals ofMgAcTDPA. ¹H NMR (400 MHz, D20): δ, ppm 2.68 (t, —S—CH2), 2.42 (t,—C(═O)CH₂), 1.87 (s, —C(═O)CH₃). Elemental analysis (found: C, 34.33; H,5.45; Mg, 6.01; S, 12.51; calculated, based on chemical formulaC₅₈H₁₁₀Mg₅O₅₂S₈: C, 34.53; H, 5.50; Mg, 6.02; S, 12.71).

The crystals were hygroscopic and converted to caramel-like, pasty solidon standing in an open jar at 80% relative humidity. The original drycrystals of the MgAcTDPA material were subjected to ¹H NMR (FIG. 4),elemental (FIG. 5) and TGA/DSC (FIG. 6) analyses. Thermogravimetricanalysis (TGA) and simultaneous differential scanning calorimetry (DSC)were conducted using a Q600 TGA/DSC instrument (TA Instruments, Inc.).Samples were subjected to heating scans (10 or 20° C/min) in atemperature ramp mode under nitrogen atmosphere.

B. NMR Spectroscopy

Integration of the proton signals (FIG. 4) revealed that α:β signalratio was 1:1, indicating the preservation of the TDPA structure in theprocess of the mixture drying. The α:γ triplet-to-singlet ratio wasmeasured to be 2.29, revealing that the thiodipropionate:acetate molarratio in the resulting MgAcTDPA salt was ca. 1.7:1.0 instead of theoriginal 1:2. The significant relative reduction in the acetate contentin the mixture occurred due to the acetic acid volatility being muchhigher than that of TDPA, thus leading to partial acetate evaporation.The signal integration further showed that the MgAcTDPA crystalsretained approximately 3.9-fold molar excess of water relative to theacetate content. corroborated these results well. The modeledcomposition of the MgAcTDPA fraction is shown in FIG. 5.

C. Thermogravimetric Analysis (TGA)

Thermogravimetric analysis (FIG. 6) shows that the properties of themixed MgAcTDPA salt resembled those of the parent MgAc₂, with themultistep, over 30 wt % endothermic weight loss due to the dehydrationabove 110° C. and decomposition over 200° C. The presence of the TDPAalong with the acetate in MgAcTDPA made the decomposition process tooccur via multiple steps. In contrast, the thermogram of MgAc waswell-defined demonstrating endothermic loss of water at around 83° C.(heat of transition, 179 J/g) and multistep endothermic decomposition inthe range of 315 to 400° C. (total heat of transition, ˜380 J/g), whichcorrelated well with the data reported previously.^(20,21)As-receivedTDPA exhibited endotherms at 105° C. and 128° C. (departure frombaseline), corresponding to the morphology change between crystallinephases and crystal melting, respectively. Decomposition of TDPA occurredendothermically at T>220° C. The TDPA presence in MgTDPA and MgAcTDPAwas evident in endothermic melting peaks with onsets at 108° C. and 112°C., respectively. Degradation of MgAcTDPA occurred via multiple stepsabove 200° C., whereas degradation of MgTDPA was sharper and occurred attemperatures above 340° C. Importantly, MgTDPA and MgAcTDPA lostapproximately 20% and 24% at 170° C., respectively, indicating thepresence of significant amount of hydrate water in these compounds.Without being bound by any theory, such water may enhance the Lewisacid/base properties and catalytic effect of magnesium thiodipropionatesin reactive organic coatings. Overall, the thermal properties such assoftening and dehydration at >150° C. and decomposition at >300° C. makethese materials suitable as additives to powder coatings, most of whichpossess a melting temperature around 150° C., and are cured at around200° C.

The content of magnesium in the MgAcTDPA sample was 2.5 meq/g, which isapproximately equal to or higher than the ion-exchange capacity of theacid polymeric ion-exchange resin AMBERLTE™ IR120 (Dow Chemical Company)ion-exchanged with magnesium.¹ The process of drying disclosed hereincan be made at temperatures from ambient to 100° C., preferably undervacuum. The initial ratio between magnesium acetate and TDPA can beconveniently varied to achieve a desired magnesium concentration andadditional components enabling desired corrosion inhibitive pigmentcharacteristics can be used. Testing of MgAcTDPA dissolution revealedunlimited aqueous solubility of the salt at room temperature. The saltalso dissolved in warm ethanol yielding at least 10 wt % concentration.

D. X-Ray Powder Diffraction (XRPD)

The MgTDPA salts resulting from the substitution reaction werecrystalline compounds as evidenced by X-ray powder diffraction (XRPD)patterns (FIG. 7). The MgTDPA_(1:1) species prepared from 1:1stoichiometric ratio of magnesium and TDPA exhibited a high degree ofcrystallinity, including the presence of low 2θ angle peaks, which pointto large, ordered unit cells. Subtraction of the amorphous contributionfrom the background and refinement of the XRPD spectrum fittingindicated a unique mixed phase structure that did not match any of thecompounds listed in the Cambridge Structural Database (CSD), includingspecific searches for existing organic magnesium salts. The mixed-fitanalysis yielded a triclinic SG1 space group, with the unit cellparameters being a(Å)=6.727, b(Å)=12.864, and c(Å)=14.645 Å,α(°)=92.567, β(°)=73.054, γ(°)=111.428. For comparison, the orthorhombiccrystal structure of TDPA grown from warm aqueous solutions that wereleft to evaporate at room temperature has been resolved usingsingle-crystal diffractometry: Pcan (Pbcn), a(Å)=5.063(1),b(Å)=8.648(1), c(Å)=18.073(2), U=791.3 Å³. The synthesis of MgTDPA viareplacement reaction (FIG. 3) in aqueous solution followed bylyophilization precluded formation of sufficiently large MgTDPAcrystals, and hence, no single-crystal diffraction peaks were visible.Nevertheless, the powder XRPD patterns confirm a unique MgTDPA_(1:1)structure that is different from the parent TDPA (FIG. 7).

Attempts to grow MgTDPA crystals by evaporating warm (40-80° C.) aqueoussolutions of the Mg/TDPA reaction mixtures lead to TDPA crystallizingseparately from magnesium salts, so that the powder XRD patterns of theproducts prepared in that fashion were indistinguishable from theoriginal TDPA patterns. The powder XRPD spectrum of MgTDPA_(5:1) speciesobtained from a 5:1 stoichiometric ratio of magnesium and TDPA startingmaterials (see Example 4) appeared to contain both broad and sharppeaks, indicating the presence of a significant fraction of amorphousphase with a second, crystalline phase embedded into the former.Elemental analysis and solubility studies demonstrated that MgTDPA_(5:1)contained at least 40 wt % of water-insoluble magnesium hydroxide. Thecrystal structure of Mg(OH)₂ (unit cell parameters, a(Å)=3.142(1),b(Å)=3.142(1), and c(Å)=4.766(2), α(°)=90, β(°)=90, γ(°)=120) has beenresolved. The somewhat broadened 20 angle peaks at 18, 37, 50, 57, and64° in the powder XRPD of MgTDPA_(5:1) clearly point to the presence of[001], [101], [102], [110] and [111] reflections, respectively, in themagnesium hydroxide crystals, which are present in the MgTDPA_(5:1)material. In contrast to the MgTDPA materials, mixed magnesium acetatethiodipropionate salt (MgAcTDPA) appeared as amorphous glassy soliddevoid of any crystalline features in its powder XRPD pattern.

E. X-Ray Photoelectron Spectroscopy (XPS)

The electronic environment of magnesium in the newly obtained magnesiumthiodipropionates can be highlighted by X-ray photoelectron spectroscopy(FIG. 8). The binding energy (BE) of Mg 2p peaks of magnesium hydroxideand that of magnesium thiodipropionate (MgTDPA_(1:1)) were observed at49.2 and 48.5 eV, respectively (FIG. 8). The BE value for Mg(OH)₂corresponded well with the value reported previously.²² The shift of BEin magnesium thiodipropionate to less electronegative values indicatesthat the Mg²⁺ cation in MgTDPA is less positive than in Mg(OH)₂. This isan interesting observation considering that Mg²⁺ cation is less positivein magnesium hydroxide than in common magnesium salts such as magnesiumchloride, nitrate or carbonate. Electron donating (Lewis base) groupssuch as OH− and, to a larger extent, thiodipropionate anions render Mg²⁺cation less positive and shift the BE to lower values. Without beingbound by any theory, the electron donating, radical trapping propertiesof thiodipropionic acid and its derivatives may explain their reportedutilization as food and polymer antioxidants, especially in synergisticmixtures with substituted phenols.

Example 2

Synthesis and Properties of Composite Pigment Particulates with anExemplary Thioether Salt

Pigment particulates were prepared from Montmorillonite K 10 clay(surface area, 220-270 m²/g, Sigma Aldrich Chemical Co.) modified by amixed magnesium acetate thiodipropionate (MgAcTDPA) salt. The initialmontmorillonite K-10 possessed the following chemical composition(average value): SiO₂ (73.0%), Al₂O₃ (14.0%), Fe₂O₃ (2.7%), CaO (0.2%),MgO (1.1%), Na₂O (0.6%), K₂O (1.9%).²³ The clay was used as received.For the material synthesis, magnesium acetate tetrahydrate (MgAc, 4.28g, 2 mmol), thiodipropionic acid (1.78 g, 1 mmol) and montmorillonite K10 (1.1 g) were dispersed in 50 mL anhydrous ethanol and the mixture wasbriefly sonicated. A cloudy, but well-dispersed suspension was obtained.The suspension was purged by nitrogen flow and then dried at 60° C. for3 days. The obtained solid was optionally ground into fine particulatesusing mortar and pestle. The fine pigment particulates were furtherground to attain a suitable particle size (<20 μm diameter) forinclusion in primer formulations.

For NMR analysis, the pigment particulates (50 mg) were suspended in 1mL D₂O and the suspension was briefly sonicated; the undissolvedparticulates were removed by centrifugation (15,000 rpm, 45 s). Thesupernatant was subjected to ¹H NMR (400 MHz) (FIG. 9). The NMR spectrumin FIG. 9 showed a water content significantly reduced compared to thespectrum of Example 1 (FIG. 4), where MgAcTDPA was obtained by dryingthe mixture of MgAc and thiodipropionic acid from water. Drying fromethanolic solution enabled removal of a substantial fraction of thehydrate water initially bound to MgAc. Elemental analysis confirmed thecomposition of the MgAcTDPA extracted from montmorillonite K 10.Elemental Analysis, found: C, 33.03; H, 5.51; Mg, 9.53; S, 6.12,calculated based on chemical formula: C₅₄H₁₁₀Mg₈O₅₉S₄: C, 32.01; H,5.47; Mg, 9.60; S, 6.33.

FIG. 10 shows TGA/DSC thermograms of montmorillonite as received and theresulting pigment composed of montmorillonite K 10 loaded with MgAcTDPA(M/MgAcTDPA) as described above. The weight loss comparison shows thatthe M/MgAcTDPA composite material consisted of approximately 69% of theorganic and residual aqueous phase that decomposed and volatilized attemperatures above 400° C., with the remaining 31% comprising clayalumosilicates. The original clay lost approximately 8-10% due tomoisture and any adsorbed VOC at temperatures at or above 180° C. andretained over 85% of the original weight at 1200° C. Endothermic peaksappearing on the heat flow thermogram of the M/MgAcTDPA materialcentered at 150° and 390° C. areas corresponded to thedehydration/acetate decomposition and thiodipropionate saltdecomposition processes, respectively. These peaks were absent in thethermogram of the as-received montmorillonite.

Example 3 Synthesis and Properties of Exemplary Thioether SaltsContaining Stoichiometric Proportions of an Alkaline Earth Metal andAcid

Salts of magnesium and thiodipropionic acid (MgTDPA_(1:1)) and magnesiumand 3,3′-dithiodipropionic acid (MgDTDPA) were prepared fromstoichiometric amounts of magnesium and corresponding acid by simplereplacement reactions (FIG. 3) as follows.

A. MgTDPA_(1:1)

Metallic magnesium powder (≥99%, mesh 325, Sigma Aldrich Chemical Co.,200 mg, 8.23 mmol) was placed in an aqueous solution of3,3′-thiodipropionic acid (97%, Sigma Aldrich Chemical Co., 1.466 g,8.23 mmol) in 30 mL DI water (initial solution pH 1.89), and the mixturewas stirred at room temperature for 24 h, at which point all magnesiumparticles completely dissolved leaving a clear solution. Hydrogenevolution ceased and pH in the solution was measured to be 5.1. Theentire solution was snap-frozen in liquid nitrogen and lyophilized for 2days until it was a constant weight. The resulting compound appeared aswhite crystalline powder of irregularly shaped particles. After 7 daysof lyophilization, the resulting compound appeared as transparentcrystalline powder. Elemental Analysis, found: C, 34.04; H, 5.30; Mg,12.04; S, 15.22, calculated based on chemical formula: C₆H₈MgS: C,35.94; H, 4.02; Mg, 12.12; S, 15.99. ¹H NMR (400 MHz, D₂O): δ, ppm 2.67(t, —S—CH2), 2.38 (t, —C(═O)CH₂).

B. MgDTDPA

Metallic magnesium powder (>99%, mesh 325, Sigma Aldrich Chemical Co.,200 mg, 8.23 mmol) was placed in an aqueous solution of3,3′-dithiodipropionic acid (99%, Sigma Aldrich Chemical Co., 1.730 g,8.23 mmol) in 30 mL DI water (initial solution pH 2.2), and the mixturewas stirred at room temperature for 24 h, at which point all magnesiumparticles completely dissolved leaving a clear solution. Hydrogenevolution ceased and pH in the solution was measured to be 5.4. Theentire solution was snap-frozen in liquid nitrogen and lyophilized for 2days until it was a constant weight. The resulting compound appeared aswhite crystalline powder of irregularly shaped particles. ElementalAnalysis, found: C, 28.51; H, 5.42; Mg, 9.61; S, 27.10, calculated basedon chemical formula: C₆H₈MgS₂: C, 30.99; H, 3.47; Mg, 10.45; S, 27.57.

Thermogravimetric analysis (FIG. 6) shows approximately 20 wt %endothermic weight loss due to the dehydration above 110° C. and a sharptwo-step decomposition in the range above 320° C. for MgTDPA_(1:1). Thehigher temperatures of the MgTDPA_(1:1) decomposition than MgAcTDPA andresemblance of the MgTDPA_(1:1) and MgAc₂ thermograms (FIG. 6) indicatea similar ionic salt nature of the magnesium thiodipropionate andmagnesium acetate compounds.

Example 4 Synthesis and Properties of an Exemplary Thioether SaltatMolar Ratios of 5 to 1

A salt of magnesium acetate and thiodipropionic acid (MgTDPA_(5:1)) wasprepared with 5-fold molar excess of magnesium relative tothiodipropionic acid as follows. Metallic magnesium powder (≥99%, mesh325, Sigma Aldrich Chemical Co., 1.0 mg, 41.15 mol) was placed in anaqueous solution of 3,3′-thiodipropionic acid (97%, Sigma AldrichChemical Co., 1.466 g, 8.23 mmol) in 50 mL DI water (initial solution pH1.89), and the mixture was stirred at room temperature for 48 h, atwhich point all hydrogen evolution ceased. pH in the solution wasmeasured to be 7.2. Magnesium hydroxide/TDPA particles were observedforming a stable suspension, which was snap-frozen in liquid nitrogenand lyophilized for 2 days until it was a constant weight. The resultingcompound appeared as white powder of irregularly shaped particles sized5-50 micron (FIG. 11). Elemental Analysis, found: C, 22.14; H, 4.54; Mg,40.01; S, 9.51, calculated based on chemical formula: C₆H₈Mg₅S: C,24.21; H, 2.71; Mg, 40.82; S, 10.77.

Thermogravimetric analysis of MgTDPA_(5:1) (FIG. 6) shows no appreciableweight loss due to water evaporation and a well-defined two-stependothermic decomposition with approximately 40% weight loss in therange above 300° C.

Example 5 Corrosion Inhibition in Aqueous Salt Media

Corrosion inhibitive properties of magnesium acetate thiodipropionate(MgAcTDPA) prepared as in Example 1 were evaluated in aqueous 3.5 wt %(0.6 M) NaCl solutions.

The electrochemical open-to-air cell (PTC1™ Paint Test Cell, GamryInstruments, Warminster, Pa.) was utilized for the potentiodynamicpolarization (Tafel tests) and electrochemical impedance spectroscopyexperiments. The electrochemical cell was composed of working electrodemade of galvanized steel (zinc-galvanized sheets of type B carbon steel,ASTM A653, total thickness 0.305 mm, working area 2.2 cm² or 15.2 cm²,McMaster Carr Supply Co., Robbinsvill, N.J.), reference Ag/AgClelectrode, and Pt wire auxiliary electrode (BASK) Corp., West Lafayette,Ind.). Prior to the immersion in the electrolyte (3.5% NaCl, pH adjustedto 5.25-5.3, 40 mL), the working electrodes were washed by acetone,ethanol, dried by nitrogen flow and polished with P1200 grit.²⁴ Theworking electrode was immersed into electrolyte containing the testedcompound at a given concentration with desired pH at 25° C. for 60 minprior to each measurement. The electrolyte was equilibrated with openair at a slightly acidic pH 5.6, which is above the pK_(a) of 4.11 ofthiodipropionic acid (TDPA). TDPA is a dicarboxylic acid with pK_(a)1and pK_(a)2 equal to 3.87 and 4.68, respectively. Hence, at pH 5.6 mostof the carboxylic groups are dissociated. The carbon steel used hereinwas coated with the average minimum coating thickness per ASTM A653being 2.0 mils (0.0508 mm) per surface. Tafel tests (ASTM GS) wereconducted using a Parstat PMC-2000 multichannel potentiostat equippedwith Versa Studio 2.50.3 software (Princeton Applied Research, OakRidge, Tenn.). Tafel tests were modeled with a ZSIMPWIN™ software forcomplex nonlinear least square analyses fitting the circuit models ofthe electrode interface to the Nyquist amplitude of 10 mV at the opencircuit potential in the frequency range of 100 kHz to 0.2 Hz.Parameters for Tafel tests were as follows: initial potential, −1.25 V(vs reference); final potential, −0.45 V; scan properties: step height,0.5 mV, step time, 2 s. In a series of measurements with the corrosioninhibiting additives, a range of the additive concentrations was studiedand the scan range was set from 150 mV below the open circuit voltage(OCV) to 200 mV more positive than the OCV, with three measurements foreach condition. The range in these measurements was limited in order tominimize the cathodic polarization causing local pH changes. The resultsof a typical potentiodynamic polarization experiment with a specimen ofgalvanized steel in 3.5% NaCl with MgAcTDPA added are shown in FIG. 12.As is seen in FIG. 12, the behavior of galvanized steel in the presenceof TDPA anions can be described as active-passive. As the potentialincreases above a certain E_(corr), the current increases exponentially,as is expected for an actively dissolving metal: Zn→Zn²⁺+2e⁻. However,at a certain Flade potential, the trend reverses and the currentdecreases because of the formation of a passive oxide film. In thepassivation region, the current density is decreasing with the potentialand increases again at a higher potential due to the breakdown of thepassive film by localized corrosion or by transpassive reactions such asoxygen evolution. The breakdown potential corresponding to theinstability of the oxide film and pitting corrosion is increased by thepresence of thiodipropionate salts. It was observed that at 1-2 mMMgTDPA_(1:1) concentrations and above in the electrolyte, the breakdownpotentials increased. Without being bound by any theory, the potentialincrease may be due to the thiodipropionate adsorption reinforcing thepassive film by blocking the Cl⁻ ions at the active site, thusinhibiting nucleation of pits.

Formation of large quantities of fluffy precipitates of white rust(approximate composition by elemental analysis, 3Zn(OH)₂.ZnCO₃.H₂O) onthe surface of a steel working electrode in the active region wasobserved in 3.5% NaCl solution without any additives, but the presenceof millimolar or higher concentrations of MgAcTDPA, MgTDPA, or TDPA tothe electrolyte solution visibly reduced the formation of white rust,instead facilitating formation of gray layers of passivated material onthe steel surface. It must be noted that the white rust, albeitsuperficial, can seriously degrade the quality and adhesion of thecoating if the surfaces of the steel are to be overpainted. In contrast,formation of the passivation layer of zinc-thiodipropionate complex canenhance the adhesion of the paint components.

In the vicinity of E_(corr) both currents are present in the specimen,but experimentally it is possible to measure only the net current. Thenet current has a single measurable polarity, either positive ornegative. At E_(corr) the net measured current is exactly zero. Thecorrosion current ( i_(corr)) is expressed as (for definitions, see FIG.13):

$i_{corr} = {\frac{\beta_{a}\beta_{c}}{2.3\left( {\beta_{a} + \beta_{c}} \right)} \times \frac{\Delta \; i}{\Delta \; E}}$

Hence, the corrosion current can be related directly to the corrosionrate (units are mils per year, or mpy) via the expression:

${{CR}\mspace{11mu} ({mpy})} = \frac{0.13\; {I_{corr}\left( {E.W.} \right)}}{d}$

where E.W. is the equivalent weight of the corroding species, g. In thiscase, the corroding species is Zn, so E.W.=32.7 g. I_(corr), is thecorrosion current density in μA/cm², and d is the density of thecorroding species. Density of zinc is 7.140 g/cm³.

From the i_(corr) values, inhibitor efficiencies (IE, %) were calculatedas (equation (1)):

${{IE}(\%)} = {\frac{{i_{corr}({control})} - {i_{corr}({inhibitor})}}{i_{corr}({control})} \times 100}$

At the end of the potentiodynamic measurements, the electrochemical cellwas disassembled and the galvanized steel electrode was gentlyair-dried. The electrode was then subjected to FTIR measurements in ATRmode. FTIR measured in the attenuated total reflection mode demonstratedthe presence of the physisorbed thiodipropionate layers on thegalvanized steel surface when MgTDPA_(1:1) was added to the 3.5% NaClelectrolyte (FIG. 14). In particular, peaks at 1720 (C═O bondedasymmetric stretch) and 1440 cm-1 (symmetric COO— stretching) indicatethe presence of the carboxylate anion on the zinc surface. FTIR of theas-synthesized magnesium thiodopropionates and TDPA are collected inFIG. 15.

Typical results of the addition of MgTDPA, MgAcTDPA and controlmagnesium acetate (MgAc) and thiodipropionic acid (TDPA) on Tafel plotsare shown in FIG. 16. To compare the effect of the additives, eachadditive's concentration in the 3.5% NaCl electrolyte (pH 5.6) wasarbitrarily set at 10 mg/mL. It was observed that all the studiedadditives reduced the icon, i.e., reduced the corrosion rate. All theanodic branches of the Tafel plots were somewhat similar prior to theonset of passivation. The anodic branches showed active zinc dissolutionand a monotonically increasing current up to very steep slopes, whichindicated a diffusion-controlled reaction rate. In the cathodic curves,representing the hydrogen evolution reaction, there exists a clearreduction in the values of the current density compared to the control(no additives), from the steel in 3.5% NaCl without additives, to sampleimmersed in the additive solutions. Varying concentration of theadditive in the bulk electrolyte changed both the cathodic and anodiccurrents (not shown), which suggested that our magnesiumthiodipropionate salts could be classified as mixed-type corrosioninhibitors. Tafel plots in FIG. 16 clearly show that MgTDPA_(1:1)reduced the Icorr values the most compared to the other additivespecies.

EIS (FIGS. 17A and 17B) was applied to further reveal the effects of thecorrosion inhibitors on the electrolyte-galvanized steel electrodeinterface and to complement the potentiodynamic polarizationmeasurements. The qualitative information was obtained using fitanalysis embedded into the software used to model the spectra, employingelectrical equivalent circuits (EECs).

Elements of the EECs are described in the legend to FIGS. 17A and 17B.The corrosion resistance of the galvanized steel surface in the presenceof the corrosion inhibitor represents the RCT+Rp sum. In the controlmeasurement without the additive, the spectrum with one time constantEEC was used, wherein the electrode resistance is represented by RCT. Anexcellent agreement between the experimental data (symbols) andcalculated model (lines) was obtained, justifying the use of theproposed EECs. Analogous EEC models have been employed previously toestimate the effects of corrosion inhibitors such as zinc benzoate,monomeric and oligomeric amines, natural products, aminoalkanoic acids,complex heterocycles, etc.

The fitting (solid curves) in FIGS. 17A and 17B demonstrated a dramatic,283-fold increase in the total resistance value R_(i)=R_(CT)+R_(p)(kΩ·cm²) in the presence of MgTDPA_(1:1) versus R_(o)=R_(CT) valuerecorded in the absence of the corrosion inhibitor. EIS measurementsenabled estimation of the corrosion inhibition efficiency:

${\eta (\%)} = {\left( {1 - \frac{R_{o}}{R_{i}}} \right) \times 100}$

The above expression (2) is equivalent to equation (1) where thecorrosion inhibition efficiency is obtained via the ratio of thecorrosion current values found via the potentiodynamic polarizationmeasurements. Both EIS and Tafel measurements are widely utilized forthe estimation of the corrosion inhibitor efficiency.

Values obtained in Tafel and EIS measurements are collected in Table 1,which affords a comparison of the corrosion inhibition effects of themagnesium thiodipropionate salts with TDPA and magnesium acetate ascontrols. MgAc₂ and especially calcium magnesium acetate (CMA, a blendof calcium and magnesium acetates resulting from the reaction of aceticacid and dolomitic limestone) are considered to be non-corrosive deicingagents and even marginally effective inhibitors of corrosion caused bychlorides.

In a separate series of experiments, rinsing the air-dried electrodewith deionized water removed the adsorbed additive, which was thenundetectable by FTIR.

Typical results of the addition of MgAcTDPA and control parent magnesiumacetate tetrahydrate (MgAc) and thiodipropionic acid (TDPA) are shown inFIG. 16. It was observed that all the studied additives reduced theI_(corr), i.e., reduced the corrosion rate. All the anodic curves weresomewhat similar prior to the onset of passivation. The anodic branchesshow active zinc dissolution and a monotonically increasing current upto very steep slopes, which indicates a diffusion-controlled reactionrate. In the cathodic curves, however, there exist a clear reduction inthe values of the current density, from the steel in 3.5% NaCl withoutadditives, to sample immersed in MgAcTDPA solution at higherconcentration. The results collected in Table 1 confirm that MgAcTDPAwas indeed the most efficient corrosion inhibitor at pH 5.3, as itreduced the rate of corrosion the most at equivalent concentrationscompared to those of either MgAc or TDPA. Suspension of MgTDPA_(5:1) wasalso quite effective in reducing the corrosion rate. Thus, it wasdiscovered that magnesium thiodipropionates or dithiodipropionate weresynergistically more efficient corrosion inhibitors than eithermagnesium acetate or thiodipropionic acid alone.

TABLE 1 Effect of magnesium acetate thiodipropionate (MgAcTDPA),magnesium acetate (MgAc₂), magnesium thiodipropionate (MgTDPA_(5:1) andMgTDPA_(1:1)), magnesium dithiodipropionate (MgDTDPA), andthiodipropionic acid (TDPA) as additives on the corrosion potential(E_(corr)), corrosion current density (I_(corr)), and corrosion rate(CR) of galvanized steel and resulting inhibitor efficiency from EIS (η,%) and from Tafel (IE, %) measurements in aqueous 3.5% NaCl solutions at25° C. Initial effective concentration of each additive in electrolytewas 10 mg/mL. [Mg²⁺] [Ac⁻]^(c) [TDPA]^(d) −E_(corr) I_(corr) Corrosion ηIE Additive^(a) pH^(b) (meq/L) (meq/L) (meq/L) (V) (μA/cm²) rate (mpy)(%) (%) None 5.3 0  0 0 1.158 180 107 N/A N/A None 5.6 0  0 0 1.099 25.815.4  0  0 MgAcTDPA^(d) 5.3  9.93 9.93 15.9 1.079 49.3 29.4 N/A N/AMgAcTDPA 5.3 41.9 41.9 67.1 1.025 13.3 7.9 N/A N/A MgAcTDPA 5.3 62.962.9 101 1.018 3.12 1.85 N/A N/A MgAcTDPA 5.6 24.8 24.8 39.7 1.067 4.062.41 80 84 MgAc₂ 5.3 71.8 144 0 0.903 62.1 37.0 N/A N/A MgAc₂ 5.6 46.693.3 0 1.059 13.5 8.03 41 48 TDPA 5.3 0  0 47.4 1.046 44.5 26.5 N/A N/ATDPA 5.3 0  0 94.8 1.049 28.4 16.9 N/A N/A TDPA 2.1 0  0 94.8 1.042 796474 N/A N/A TDPA 5.6 0  0 56.1 1.076 4.15 2.47 81 84 MgTDPA_(5:1) 5.3167^(e )   0 33.5 0.983 85.1 50.7 N/A N/A MgTDPA_(5:1) 5.6 125   0 25.01.068 7.82 4.65 72 69 MgTDPA_(1:1) 5.3 49.8 0 49.8 1.054 35.5 21.1 N/AN/A MgTDPA_(1:1) 5.6 49.9 0 49.9 1.064 1.79 1.07 99 93 MgDTDPA 5.3 40.60 40.6^(f) 1.049 63.5 37.8 N/A N/A ^(a)Initial pH in the electrochemicalcell prior to the experiment commencement. ^(b)Total magnesiumconcentration. ^(c)Acetate concentration. ^(d)Thiodipropionateconcentration. ^(e)Concentration of DTDPA. ^(f)Measurements wereperformed in triplicate, and all calculated data reported as averages (n= 3). Maximum standard deviations for η and IE values were 12% and 6% ofthe mean values, respectively.

Data in Table 1 demonstrate that MgTDPA_(1:1) is a more effectivecorrosion inhibitor for galvanized steel than either TDPA or MgAc₂.Without being bound by any theory, the increased effectiveness may bedue to the synergistic effect afforded by the presence of bothwater-soluble TDPA anions and magnesium cations when MgTDPA_(1:1) isadded to the electrolyte. The presence of acetate in the MgAcTDPA mixedsalt lowered the effective concentration of magnesium and TDPA ionscompared to MgTDPA_(1:1). Without being bound by any theory, thesefeatures may have lowered the corrosion inhibition efficiency ofMgAcTDPA. Likewise, MgTDPA_(5:1) was only fractionally soluble in theelectrolyte and yielded a suspension rather than solution, whichcertainly lowered the concentration of the TDPA ions available foradsorption on the steel surface. Correlation between η (%) and IE (%)values was found satisfactory, with η having higher uncertainty ofdetermination due to the data fitting procedure.

In addition to the newly discovered inhibitors, such as the MgTDPA_(1:1)inhibitor, there are other, related corrosion inhibitors such as metalcarboxylates, the effects of which on steel have been studiedpreviously. Analogously to the magnesium thiodipropionate described inthe present work, the anodic inhibitory effect of carboxylates has beencombined with cathodic inhibitory cations, such as cerium, lanthanum andother rare earth metals and zinc. For example, decanoic acid, consideredto be an efficient corrosion inhibitor, enabled inhibition efficiencyη=83.5% on galvanized steel at concentration 44.7 mM, in electrolytecontaining 0.0165 wt % NaCl (pH not stated). At that concentration ofdecanoic acid the η values plateaued, yet the total salt concentrationwas approximately 100-fold lower than in the experiments describedherein. Decanoic acid was approximately as efficient a corrosioninhibitor as TDPA (compare with data in Table 1), but less efficientthan MgTDPA_(1:1). Zinc decanoate demonstrated inhibition efficiencyη=65% on carbon steel. Zinc decanoate has limited aqueous solubility ofonly 0.026 mM.

Concentration dependencies of the inhibitor efficiency IE (%) for TDPA,MgAcTDPA and MgTDPA_(1:1) shown in FIG. 18 were of characteristicsaturation type, with the IE values plateauing at C_(TDPA)>30 mM. Theinhibitor efficiency was related to the adsorption of TDPA on the steelsurface and was reversible (physisorption), with the layers of theadsorbed thiodipropionate readily soluble in fresh electrolyte.Therefore, assuming that IE is proportional to the steel surfacecoverage upon TDPA adsorption, the experimental data in FIG. 18 wereplotted in the form of Langmuir adsorption isotherm (equation (3)):

$\frac{C_{TDPA}}{q} = {\frac{1}{K_{a}} + C_{TDPA}}$

where Ka is the equilibrium constant for the adsorption-desorptionprocess and q=0.01.IE.

The agreement between the Langmuir isotherm interpretation (equation (3)above) and experimental data was excellent, with all fitted lines beinglinear (R²>0.995 in all cases) and the corresponding slopes were closeto unity (1.03±0.06), as is theoretically predicted. The Y-axisintercept of the lines in FIG. 19 yielded K_(a) in the range 150-190M⁻¹, which affords an estimate of the corresponding standard Gibbs freeenergy (Mg) of the thiodipropionate adsorption from the expression (4):

−ΔG _(a) ⁰ =RT ln(c _(solvent) K _(a))

where c_(solvent)=55.5 M is the water concentration, R=8.314 J/mol·K isthe gas constant and T=298 K is the absolute temperature.

The data yielded −ΔG_(a) ⁰ values of 22.4-23.0 kJ/mol, which is close tothe range of −20 kJ/mol typically attributed to physisorption viaelectrostatic interaction between the charged carboxylates and thecharged metal. Spontaneity of the adsorption process is supported by thenegative G_(a) ⁰ values indicating that the corrosion inhibitor speciesform stable layers on the steel surface.

In summary, it was discovered that magnesium thiodipropionate salt is anefficient corrosion inhibitor for galvanized steel in 3.5% NaClsolutions of moderately acidic pH, acting via formation ofthiodipropionate layers on the steel surface. The cathodic protectioneffect of magnesium ions can be seen in augmented inhibition efficiencyof MgTDPA compared to that of thiodipropionic acid.

Example 6 Effect of Exemplary Composites on the Rate of Curing of EpoxyResins Determined by Gel Time Method

Tested an epoxy two-part curing system comprising ARALDITE® LY8601 resinand ARADUR® 8602 hardener, both supplied by Hutsman Advanced Materials.ARALDITE® LY8601 is composed of bisphenol A epoxy resin (60-100%),glycidylether of C₁₂-C₁₄ alcohols (7-13%), and butylphenyl glycidylether (3-7%), whereas ARADUR® 8602 is composed principally ofdiethylenetriamine (13-30%), polyoxypropylene diamine (13-30%),4-nonyl-phenol (7-13%), triethanolamine (3-7%), and2-(2-aminoethylamino)ethanol (0.1-1%). The ARALDITE® LY8601/ARADUR® 8602components taken at 4:1 w/w ratio result in epoxy curing infusion system(ECIS) with initial nominal viscosity of 175 cP.²⁵ The rheologicalmeasurements were conducted using a controlled stress ARES-G2 Rheometer(TA Instruments) with a parallel-plate geometry system (steel plate, 25mm diameter, equipped with a solvent trap), gap set at 1 mm. Time sweeposcillatory shear experiments were conducted at 1 Hz. Preliminaryfrequency and time sweeps were conducted with the control ECIS mixtureto find optimum experimental, stress-strain linearity and temperatureconditions. The empty chamber was preheated to the gel time testtemperature set at various temperatures ≥60° C. In the experiments,finely powdered composite pigment particulates of montmorillonite withmagnesium acetate thiodipropionate (M/MgAcTDPA), which were prepared asin Example 2, at 5 wt % or 8 wt % solids or MgTDPA_(1:1) as prepared inExample 3A at 5 wt % were blended with the ARALDITE® LY8601/ARADUR® 8602(4:1 w/w) to result in homogeneous suspensions of solids upon mixing.After vigorous mixing, the suspension or the control ECIS resin wasquickly deposited on preheated plate, the upper plate was quicklylowered to a set gap and the excess fluid was wiped up and removed fromthe plate edges. Typical gel time determination results are shown inFIG. 20.

The two-component system is a relatively low-viscosity liquid that, uponrapid mixing, is capable of solubilizing magnesium thiodipropionates atambient temperature without gelling, with or without the use of reactivediluents such as 1,4-butanediol diglycidyl ether and the like. The gelpoint (onset of gelation, t_(gel)) of that liquid is very sensitive totemperature and additives. The onset of gelation was measured usingcontrolled stress rheometry at a given temperature according to theWinter-Chambon criterion,²⁶ at the crossover of the storage and lossmoduli (G′=G″; loss angle δ=45°) (FIG. 21). The gel times were measuredto be 424 s for the modified and 513 s for the original resincompositions, respectively. The results of the isothermal rheologicalt_(gel) measurements in the 60-100° C. temperature range are shown inFIG. 21. The linearity of the plots in FIG. 21 indicated that theArrhenius model held very well. The magnesium thiodipropionates indeedlowered the t_(gel) values throughout the temperature range studied.Apparent activation energy values for the fast-curing epoxy-amine systemwithout additives were 39.2 kJ/mol and at 5 wt % loading, MgTDPA andMgAcTDPA lowered apparent activation energy of curing to 27.8 and 29.3kJ/mol, respectively. These results demonstrate that the MgAcTDPAcomposite with montmorillonite accelerated the crosslinking curingreaction between the epoxy resin and amine hardener in the two-componentresin system utilized for coatings and advanced composites. Moreover,the additive pigment composite particles altered the initial viscosityof the resin compositions, acting as useful rheology modifiers. Theseresults demonstrated that magnesium thiodipropionates retain the usefulfeature of their parent TDPA, i.e., they act as curing accelerators ofheterocyclic compounds, oxiranes and benzoxazines, widely employed ascomponents of organic coatings.

Example 7 Effect of an Exemplary Thioether Salt on the Rate of Curing ofBenzoxazine Resins

The accelerating effect of magnesium acetate thiodipropionate (MgAcTDPA)on curing polymerization of bisphenol-A thermosetting benzoxazine resinwas demonstrated. The resin sample was obtained from Huntsman AdvancedMaterials (product designation, XU35610). Poly(bis-benzoxazine)s are afamily of thermosetting coating components that are polymerized throughstep growth ring-opening polyaddition from bis-benzoxazine monomers suchas XU35610 (FIG. 22). That is, homopolymeriztion and crosslinking of thebenzoxazine resin (a model system) are depicted in FIG. 22. The monomersare the products of the Mannich reaction between a bisphenol,formaldehyde, and a primary amine. For the coating applications, thetemperature, rate and extent of curing are very important that affectthe physical, chemical and mechanical properties of the coatings.Compounds that lower the temperature of curing are termed accelerators.

As received XU35610 was dissolved in ethanol/methyl ethyl ketone (MEK)(90:10 v/v) mixture and recrystallized after solvent evaporation undervacuum. A homogeneous blend of XU35610 resin and magnesiumthiodipropionate (either MgTDPA_(1:1) as prepared in Example 3A orMgAcTDPA as prepared in Example 1) was prepared as homogenous solutionin ethanol/MEK (90:10 v/v) followed by mixing and solvent evaporationunder vacuum at 60° C. Concentrations of magnesium thiodipropionates inthe blends were set at 10 mol % relative to the benzoxazine monomer (MW463 Da). The resulting material was finely ground and was placed inhermetically sealed aluminum pans. Differential scanning calorimetry(DSC) isotherms were measured under flowing nitrogen using a DiscoveryDSC (TA Instruments) with modulated temperature amplitude at heatingramp rates (β=dT/dt) varying in the 2-15° C./min range. Curing peakmaxima were determined using instrument software. The DSC (FIG. 23) datademonstrated that the onset of curing reactions in the benzoxazine resinwas significantly (ca. 46° C.) lowered by the addition of MgAcTDPA,thereby confirming the curing accelerator action of the salt.

Typical DSC thermograms of the original benzoxazine and magnesiumthiodipropionate/benzoxazine blends (FIG. 24) show the effect of theadditives on the onset of the polymerization exotherm, which issignificantly lower in the presence of magnesium thiodipropionates; theexotherm's end point is barely affected. That is, the exotherms weresignificantly broadened in the presence of additives and the peaks movedto lower temperatures. Without attempting arbitrarily to deconvolve thepeaks into various thermal events, it was observed that the peak maximawere at 220° C., 204° C., and 178° C. for exotherms without additives,with MgAcTDPA, and with MgTDPA as additives, respectively. Similareffects on benzoxazine polymerization were previously reported withTDPA, where the onset of the polymerization and the peak maxima moved tolower temperatures, whereas the end point of the exotherm did not move,leading to peak broadening. Without being bound by any theory, suchobservation has been interpreted as TDPA having the greatest impact onthe initial stages of the polymerization such as ring opening, with thesubsequent processes associated with cross-linking being affected to alesser degree. Using variable heating rate method (e.g., “Ozawacorrected”), the Arrhenius activation energies of the benzoxazinemonomer were estimated to be 88.6 kJ/mol (FIG. 25), which is within therange of previously reported values ranging from 81.4 to 93.7 kJ/moldepending on the monomer's degree of purification by crystallization. At10 mol % loading, MgTDPA and MgAcTDPA lowered apparent activation energyof benzoxazine polymerization to 63.7 and 69.1 kJ/mol, respectively, inline with the notion of the salts acting as catalysts. Similar effectsof additive presence have been previously observed with TDPA and4,4′-thiodiphenol, both of which are recognized as benzoxazinepolymerization accelerators.

Example 8

Epoxy-Amine Coating Compositions with Cathodic Disbondment InhibitionComponents

An exemplary two-part epoxy-amine coating was prepared from maincomponents shown in FIG. 26, 4,4′-diaminophenylsulfone (DAS, SigmaAldrich) and tetrafunctional epoxy (ARALDITE® MY 721 from HuntsmanAdvanced Materials).

Preparation

Coupons of galvanized steel (ASTM A653, total thickness 0.305 mm,working area 2.2 cm²) were pre-treated by washing by acetone, polishingand drying as described in Example 3. The steel coupons were kept at 50°C. prior to coating. 4,4′-Diaminophenylsulfone (0.5 g) was mixed withARALDITE® MY721 epoxy (0.85 g), 310 mg of ARADUR® 125 BDB polyamidoaminehardener (Huntsman Advanced Materials), multiwalled carbon nanotubes(100 mg, Sigma Aldrich) and 310 mg of finely powdered composite pigmentparticulates of Montmorillonite K 10 clay with magnesium acetatethiodipropionate (M/MgAcTDPA) prepared as described in Example 2. Theresulting black paste was thoroughly mixed by spatula and diluted asneeded by 3-5 mL acetone.

The steel coupons pre-heated at 50° C. were painted by a brush on allsides by the above black paste, leaving an unpainted strip on top. Thecoupons were hung by crocodile clip/wire by the unpainted strip and keptat 80° C. in an oven for 36 h. The resulting black coating wasapproximately 0.3 mm thick, hard and scratch-resistant. For testing, thecoupons were kept completely immersed into aqueous 3.5% NaCl for 60 daysat ambient temperature.

The coated and control uncoated coupons were subjected toElectrochemical Impedance Spectroscopy (Nyquist) tests [ASTM(D01.27.32)] after 0.5-h (initial) and 60 days of immersion in 3.5% NaClsolution (FIGS. 27A and 27B). Due to the presence of the relativelyhydrophilic polyamidoamine hardener, conductive carbon nanotubes andwater-soluble MgAcTDPA, our coating rapidly developed considerableconductivity due to the electrolyte penetration. After a short amount oftime (0.5 h), water penetrated into the coating and formed a newliquid/metal interface under the coating. This interface containedpartially dissolved MgAcTDPA modeled as a double-layer capacitor inparallel with a kinetically controlled charge-transfer reaction whenMg(OH)₂ was formed, which prevented delamination and the coatingdelamination/failure.

After the prolonged exposure to the salt solution, the coupons wereair-dried at ambient temperature for visualization.

Visual observation after 60 days (FIG. 28) showed that the coatingprovided adequate protection to the coupons, as the coating stayedintact; no delamination was observed. Occasional pitting spots wereobserved on the uncoated strip surfaces of the coupon that were leftimmersed for 60 days, but no corrosion propagation underneath thecoating or delamination of the polymer layers was observed. In contrast,the uncoated coupon left in salt solution for 60 days developed largeamounts of zinc patina and white rust.

Example 9

Hydrophobic Epoxy-Amine Coating Compositions with Cathodic DisbondmentInhibition Components

Coupons of galvanized steel (ASTM A653, total thickness 0.305 mm,working area 2.2 cm²) were pre-treated by washing by acetone, polishingand drying as described in Example 3. The steel coupons were kept at 50°C. prior to coating.

4,4′-Diaminophenylsulfone (2.0 g) and bisphenol A propoxylate diglycidylether (2.0 g, Sigma Aldrich) were mixed with ARALDITE® MY721 epoxy (2.0g) and 5 mL of a solution of MgAcTDPA (prepared as in Example 1) inethanol (30 wt %). The resulting yellowish transparent blend wasthoroughly mixed by spatula and diluted as needed by ethanol forpainting.

The steel coupons pre-heated at 50° C. were painted by a brush on allsides by the above viscous solution, leaving an unpainted strip on top.

Control coating was formulated without MgAcTDPA. Namely,4,4′-diaminophenylsulfone (2.0 g) and bisphenol A propoxylate diglycidylether (2.0 g, Sigma Aldrich) were mixed with ARALDITE® MY721 epoxy (2.0g) and 5 mL absolute ethanol. The resulting yellowish transparentsolution was thoroughly mixed by spatula and painted onto pre-heatedsteel coupons.

The coupons were hung by crocodile clip/wire by the unpainted strip andkept at 80° C. in an oven for 48 h. The resulting transparent yellowishcoating was approximately 1 mm thick, hard and scratch-resistant. Fortesting, the coupons were kept completely immersed into aqueous 3.5%NaCl for 30 days at ambient temperature.

Visual observation after 30 days (FIG. 29) showed that the coating thatcontained MgAcTDPA provided adequate protection to the coupons, as thecoating stayed intact; no delamination was observed. The control coatingprepared without MgAcTDPA was totally delaminated with the polymerlayers flaking off and separating from the steel surface. The metalsurface underneath the control coating was completely covered with darkzinc patina. The coating prepared with MgAcTDPA allowed maintenance ofshiny metal layer underneath without visible corrosion.

Example 10 Powder Compositions of an Exemplary Thioether Salt

Powder compositions for electrodeposition on galvanized steel optimizedfor ease of compounding, temperature of epoxy-amine hardener curing,electrodeposition and adhesion to steel were prepared as follows.Powdered Araldite GT 6259 resin compounded with montmorillonite K10,carbon black, and magnesium thiodipropionate (MgTDPA_(1:1)) were milledat 50° C. for 1 h using a planetary ball mill, then dry ice andcrosslinker dicyandiamide were added to the blend and the resultingmixture was pulverized using a high-speed powder blender.

The final blend compositions are shown in Table 2. The powders weresieved at room temperature using a #200 mesh sieve, resulting inparticles sized below 70 micron (FIG. 11). The release of magnesium fromthe powder compositions was tested as follows: a known amount ofas-prepared powder (10 to 20 mg) containing 6.1 wt % MgTDPA wasdispersed in 10 mM Tris buffer (3 mL) with pH adjusted in the 6-10range. The dispersion was briefly sonicated and then gently shaken atroom temperature overnight. The liquid was then separated from thesolids by a syringe membrane filter (Millipore, d_(p)ore 0.45 μm) andwas assayed for magnesium content in a commercial laboratory by ICP-AESspectrometry. The measurements were conducted in triplicate.

TABLE 2 Powder coatings compositions Epoxy Carbon resin Crosslinkerblack Montmorillonite MgTDPA (wt %) (wt %) (wt %) (wt %) (wt %) Control75.7 15.2 8.9 0.2 0 Test 72.7 12.1 8.9 0.2 6.1 coating

Panels of galvanized steel (zinc-galvanized sheets of type B carbonsteel, ASTM A653, 4″×3″×0.0150″) were solvent-brushed according to ASTMD609-17^(ref) and kept at 400° F. immediately prior to the powderelectrodeposition. The powders were deposited on preheated steel panelsusing an Eastwood Dual-Voltage HotCoat Powder-Coating Gun at 25 kV andbaked in an electrical oven at 400° F. for 20 min and 375° F. for 15min. The resulting coatings were 3.8-4.0 mil (97-102 μm) thick.

Magnesium thiodipropionates exhibit corrosion inhibitive properties inaqueous media, with MgTDPA_(1:1) species being efficient. Given thesuitable thermal properties of MgTDPA_(1:1) and its aqueous solubilityand dispersibility in epoxy resins, its performance was examined inpowder coatings. Incorporation of corrosion inhibitors into a polymericmatrix for the purpose of limiting cathodic disbondment is a complextask, given the opposing requirements for the corrosion inhibitoraccessibility for water in order to function versus the protective,barrier properties of the coating's polymer matrix. In order toimplement powder electrodeposition while still enabling water access tomagnesium thiodipropionate, the salt was physically blended, withoutmelting, with the epoxy resin and dicyandiamide (latent crosslinker withhigh melting point) as the two major components. The composition alsocontained specialty carbon black and montmorillonite clay that enhancedthe blended powder dispersibility. The accessibility of the powdercomposition to water was investigated as a function of pH by quantifyingthe fraction of magnesium initially present in MgTDPA that is releasedfrom the powder in contact with water using ICP (FIG. 30).

At pH<9, essentially all of Mg initially loaded into the powdercomposition with MgTDPA by powder blending was released into the aqueousbuffer. At pH>9.3, Mg²⁺ produced by dissociated MgTDPA formed insolubleMg(OH)₂, which was removed by filtration along with the powder material.These experiments indicate that when a corrosive cathodic O₂ reductionoccurs on the interface between metal and the coating (i.e., in thedelamination front), the magnesium cations dissociating from theMgTDPA-containing coating will exhibit an anticorrosion action bystopping propagation of the corrosion front on the metal-coatinginterface because of the formation of the barrier Mg(OH)₂ precipitate:

O_(2 (g))+2H₂O+4e⁻→4OH⁻ _((aq))

Mg²⁺+2H₂O

Mg(OH)_(2↓)+2H⁺

Following the coating processes, the coated steel panels were scribed ina controlled fashion and subjected to the immersion and cyclicalsalt-spray tests (see Examples 11 and 12).

Example 11

Immersion Tests with an Exemplary Thioether Salt

Prior to the commencement of the immersion test, the coated panels werescribed with a scalpel blade making 100 μm-wide and 3 cm-long cutsexposing the bare steel surfaces. The tests were conducted by completeimmersion of the coated panels in 3.5 wt % aqueous NaCl solutions (pH5.25) at 25° C. Quantitative measurements of the scribe creep wereconducted at the conclusion of the immersion tests after 60 days.Following the 60-day immersion, the panels were gently rinsed bydeionized water, air-dried and any flaked or blistered coating along theedges of the scribe was removed using an adhesive tape according to ASTMD3359.^(ref) Scribe creep measurement was performed by taking eightmeasurements along the length of the scraped scribe. The creep wasmeasured edge-to-edge of the scribe using digital calipers and 3×magnifying glass, then averaged for each panel. Each type of panel (i.e.with and without the corrosion inhibitor) was measured in triplicateusing three distinct panels, and the results were averaged among thepanels of the same type.

The scribed areas were visualized using SEM images (60-day immersiontests, FIGS. 31A, 31B, 32A, and 32B), which showed that the scribes wereinitially identical in width but became significantly (˜30 to 60%) widerfor the coatings devoid of the corrosion inhibitor. The scribe creep(widening) was used as a quantifiable parameter of the coatingdelamination in immersion corrosion tests (FIG. 33). The average scribecreep in the panels coated without the corrosion inhibitor was 2.4- to2.6-fold larger than with an analogous coating containing the corrosioninhibitor magnesium thiodipropionate. These results provided anunequivocal proof of the protective action of magnesium thiodipropionatein the developed epoxy-amine powder coatings.

Example 12

Cyclical Salt-Spray Tests with an Exemplary Thioether Salt

The powder coatings prepared with and without the corrosion inhibitor,MgTDPA_(1:1), were subjected to six cyclical tests in a commerciallaboratory according to ISO 11997.^(ref) Each cycle consisted ofconsecutive wet (salt fog), dry, and humidity exposures. That is, eachstandard cycle corrosion test was set as a combination of neutral saltspray exposure according to ASTM B 117 and ISO 9227 certified tests,100% condensing humidity according to ISO 6270-2, drying and dwelling.One full corrosion cycle was a week in duration. The coated panels(4″×3″×0.0150″) were scribed using a van Laar Model 426 scratching toolwith spherical tungsten scratch needle (Erichsen GmbH & Co., Germany).Ferrous rust run-offs were not observed on the panels after 6 cycles.There was no blistering away from the scribe per ASTM D1654 in any ofthe tested panels. However, the appearance of white rust powderydeposits was observed on the surface of the scribes as well as in thewash-outs. Following the six cycles, the panels were gently rinsed bydeionized water, air-dried and any flaked or blistered coating along theedges of the scribe was removed using an adhesive tape according to ASTMD3359. Scribe creep measurement was performed by taking eightmeasurements along the length of the scraped scribe. The creep wasmeasured edge-to-edge of the scribe using digital calipers and 3×magnifying glass, then averaged for each panel. Each type of panel (withand without the corrosion inhibitor) was measured in triplicate usingthree distinct panels, and the results were averaged among the panels ofthe same type.

The scribe creep (widening) was used as a quantifiable parameter of thecoating delamination in industry-standard cyclic corrosion tests (FIG.33). The average scribe creep in the panels coated without the corrosioninhibitor was 2.4- to 2.6-fold larger than with an analogous coatingcontaining the corrosion inhibitor magnesium thiodipropionate. Theseresults provided an unequivocal proof of the protective action ofmagnesium thiodipropionate in the developed epoxy-amine powder coatings.

Developments in the field of “green” corrosion inhibitors are directedtoward inexpensive, effective molecules of minimal negativeenvironmental impact. In that regard, the magnesium thiodipropionatesdisclosed herein, which are prepared in water by either a simplereplacement reaction of magnesium metal with thiodipropionic acid (TDPA)or metathesis reaction, represent promising entries in the greencorrosion inhibitors arsenal. TDPA is a non-toxic, monolayer-forming,non-irritating dicarboxylic acids that is catabolized by microbes,whereas magnesium is more abundant and certainly less expensive thanrare earths, carboxylates of which are considered to be green corrosioninhibitors. Yet, magnesium thiodipropionates are quite effectivecorrosion inhibitors in aqueous media and, for the first time, have beenshown here to lower delamination of the powder coatings. This, combinedwith the observation that magnesium thiodipropionates acceleratebenzoxazine polymerization and curing of the epoxy resin with aminehardeners, represents a rarely found synergism of functionalities usefulwherever coatings are applied.

CITED REFERENCES

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INCORPORATION BY REFERENCE

All U.S. patents and U.S. and PCT published patent applicationsmentioned in the description above are incorporated by reference hereinin their entirety.

EQUIVALENTS

Having now fully described the present invention in some detail by wayof illustration and example for purposes of clarity of understanding, itwill be obvious to one of ordinary skill clin the art that the same canbe performed by modifying or changing the invention within a wide andequivalent range of conditions, formulations and other parameterswithout affecting the scope of the invention or any specific embodimentthereof, and that such modifications or changes are intended to beencompassed within the scope of the appended claims.

1. A curable coating composition, comprising: (a) a salt comprising adivalent alkaline earth metal cation and an anionic thioether compound;(b) a curing agent or a mixture of curing agents; and (c) one or morecurable organic resins.
 2. The composition of claim 1, wherein thedivalent alkaline earth metal cation is selected from the groupconsisting of Ca²⁺, Mg²⁺, Sr²⁺, and Ba²⁺. 3-6. (canceled)
 7. Thecomposition of claim 1, wherein the salt has the following structuralformula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; and X is selected from the group consisting of H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R². 8-11.(canceled)
 12. The composition of claim 1, wherein the salt has thefollowing structural formula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; X is selected from the group consisting of absent, H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R²; and n is 1or
 2. 13-15. (canceled)
 16. The composition of claim 1, wherein theratio of the divalent alkaline earth metal cation to the anionicthioether compound is from about 50:1 to about 0.1:1. 17-22. (canceled)23. The composition of claim 1, wherein the salt is from about 0.1% toabout 80% by weight, based upon total solids weight of the composition.24-26. (canceled)
 27. The composition of claim 1, wherein the curingagent or the mixture of curing agents comprises an amine, anamido-amine, a phenol, a carboxylic anhydride, or a mercaptan. 28-38.(canceled)
 39. The composition of claim 1, further comprising: (i) apigment; or (ii) an additive.
 40. (canceled)
 41. The composition ofclaim 39, wherein the composition comprises a pigment selected from thegroup consisting of carbon nanotubes, titanium dioxide, montmorillonite,iron oxide, aluminum, bronze, phthalocyanine blue, and a mixturethereof. 42-45. (canceled)
 46. The composition of claim 1, furthercomprising an additive.
 47. The composition of claim 46, wherein theadditive is selected from the group consisting of a dye, a flow controlagent, a dispersant, a thixotropic agent, an adhesion promoter, anantioxidant, a light stabilizer, a curing catalyst, an anticorrosionagent, and a mixture thereof. 48-49. (canceled)
 50. A method ofanticorrosive treatment, comprising: providing a substrate, wherein saidsubstrate is a ferrous substrate; coating the substrate with acomposition comprising: B4871949.1 (a) a salt comprising a divalentalkaline earth metal cation and an anionic thioether compound; (b) acuring agent or a mixture of curing agents; and (c) one or more curableorganic resins; thereby preventing or reducing corrosion of thesubstrate.
 51. A method of preventing or reducing corrosion on asurface, comprising applying to the surface a coating, comprising: (a) asalt comprising a divalent alkaline earth metal cation and an anionicthioether compound; (b) a curing agent or a mixture of curing agents;and (c) one or more curable organic resins; thereby preventing orreducing corrosion of the surface.
 52. (canceled)
 53. The method ofclaim 50, wherein the substrate is selected from the group consisting ofsteel, carbon steel, galvanized steel, and pig iron. 54-60. (canceled)61. The method of claim 50, wherein the salt has the followingstructural formula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; and X is selected from the group consisting of H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R². 62-65.(canceled)
 66. The method of claim 50, wherein the salt has thefollowing structural formula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; X is selected from the group consisting of absent, H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R²; and n is 1or
 2. 67-80. (canceled)
 81. The method of claim 50, wherein the curingagent or the mixture of curing agents comprises an amine, anamido-amine, a phenol, a carboxylic anhydride, or a mercaptan. 82-114.(canceled)
 115. The method of claim 51, wherein the salt has thefollowing structural formula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; and X is selected from the group consisting of H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R².
 116. Themethod of claim 51, wherein the salt has the following structuralformula:

wherein R is selected from the group consisting of divalent(C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl,heteroaralkyl, and (C₂-C₆)alkenyl; R¹ is selected from the groupconsisting of divalent (C₁-C₆)alkyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, aralkyl, heteroaralkyl, and (C₂-C₆)alkenyl; R² is hydrogenor (C₁-C₂₀)alkyl; X is selected from the group consisting of absent, H,halogen, (C₁-C₂₀)alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, (C₂-C₂₀)alkenyl, —OR², —SR², —N(R²)₂,—C(O)N(R²)₂, —C(O)N(R²)((C₁-C₂₀)alkylene)N(R²)₂, and —C(O)R²; and n is 1or
 2. 117. The method of claim 51, wherein the curing agent or themixture of curing agents comprises an amine, an amido-amine, a phenol, acarboxylic anhydride, or a mercaptan.